LIBRARY OF CONGRESS, 



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aJAxS" 



Human Physiology. 



BRUBAKER. 



? QUIZ COMPENDS. ? 

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? QUIZ COMPENDS. ? No. 4. 



COMPEND 



OF 



Human Physiology. 



ESPECIALLY ADAPTED FOR THE USE OF 
MEDICAL STUDENTS. 



• 



ALBERT P. BRUBAKER, M.D., 

Demonstrator of Physiology in the Jefferson Medical College; Member 
of the Pathological Society. 




PHILADELPHIA : 

P. BLAKISTON, SON & CO., 

1012 Walnut Street. 
1883. 



C9-* a 



3 



Entered according to Act of Congress, in the year 1882, by 

P. BLAKISTON, SON & CO., 

In the Office of the Librarian of Congress, at Washington, D. C. 



TO MY FATHER, 

HENRY BRUBAKER, M.D., 

THIS LITTLE VOLUME 

IS AFFECTIONATELY INSCRIBED. 



TABLE OF CONTENTS. 



PAGE 

Introduction 9 

Chemical Composition of the Body 10 

Structural Composition of the Body 14 

Food 17 

Digestion 20 

Absorption.. 25 

Blood 29 

Circulation of Blood 34 

Respiration , 39 

Animal Heat 44 

Secretion , 46 

Mammary Glands 49 

Vascular or Ductless Glands 50 

Excretion 52 

Kidney 52 

Liver 57 

Skin 60 

Nervous System , 63 

Spinal Nerves 65 

Properties and Functions of Nerves 67 

Cranial Nerves 69 

Spinal Cord 82 

Medulla Oblongata 88 

Pons Varolii , 90 

Crura Cerebri 91 

Corpora Quadrigemina 91 

Corpora Striata and Optic Thalami 92 

vii 



Vlll TABLE OF CONTENTS. 

PAGE 

Cerebellum 93 

Cerebrum .........v. 95 

Sympathetic Nervous System 100 

Sense of Touch 103 

Sense of Taste 104 

Sense of Smell 106 

Sense of Sight 107 

Sense of Hearing , 112 

Voice and Speech 117 

Reproduction. 119 

Generative Organs of the Female 11.9 

Generative Organs of the Male 122 

Development of Accessory Structures 123 

Development of the Embryo 128 



COMPEND 

OF 



HUMAN PHYSIOLOGY 



Physiology, from wuaiq nature, and X6yo<;. a discourse, in its origi- 
nal application embraced the study of all natural objects, inorganic as well 
as organic. In its modern application physiology signifies the study of 
life ; investigating the vital phenomena exhibited by all organic bodies, 
vegetable and animal. 

It may be divided into — 

1. Vegetable physiology, which treats of the phenomena manifested by 
the several structures of which the plant is composed. 

2. Animal physiology, which treats of the phenomena manifested by the 
organs and tissues of which the animal body is composed. 

Human Physiology is the study of the functions exhibited by the 
human body in a state of health. 

A function is the action of an organ or tissue. 

The Functions of the Human Body may be classified into three 
groups, viz. : — 

1. Nutritive functions, which have for their object the preservation of 
the individual; e. g., digestion, absorption, blood circulation, respira- 
tion, assimilation, animal heat, secretion and excretion. 

2. Animal functions , which bring the individual into conscious relation- 
ship with external nature; e. g., sensation, motion, language, mental 
and moral manifestations. 

3. Reproductive function, by means of which the species is preserved. 
The facts of human physiology have been determined by means of 

anatomy, chemistry, pathology, comparative anatomy, vivisection, the 
application of physics, etc. 

The Body may be studied from a chemical and structural point of view. 
B 9 



10 HUMAN PHYSIOLOGY. 

CHEMICAL COMPOSITION OF THE HUMAN 

BODY. 

Of the sixty-four chemical elements, about sixteen enter into the 

composition of the body, in the following proportions : — 

Oxygen 72.00 ......O. H. and C. are found in all the tissues and 

Hydrogen 9.10 fluids of the body, without exception. 

Nitrogen 2.50 0. H. C. and N. found in most of the fluids 

Carbon, I 3-5° and all tissues except fat. 

Sulphur 147 .In fibrin, casein, albumen, gelatin; as potas- 
sium sulpho-cyanide in saliva; as alkaline 
sulphate in urine and sweat. 

Phosphorus 1.15 In fibrin and albumen ; in brain ; as tri-sodium 

phosphate in blood and saliva, etc. 

Calcium !-30 As calcium phosphate in lymph, chyle, blood, 

saliva, bones and teeth. 

Sodium. .10 As sodium chloride in all fluids and solids of 

the body, except enamel; as sodium sul- 
phate and phosphate in blood and muscles. 

Potassium 026 As potassium chloride in muscles; generally 

found with sodium as sulphates and phos- 
phates. 

Magnesium 001 Generally in association with calcium, as phos- 
phate, in bones. 

Chlorine 085 In combination with sodium, potassium and 

other bases, in all the fluids and solids. 

Fluorine 08 As calcium fluoride in bones, teeth and urine. 

Iron 01 In blood globules; as peroxide in muscles. 

Silicon a trace In blood, bones and hair. 

Manganesium, a trace Probably in hair, bones and nails. 

Of the four chief elements which together make up 97 per cent, of the 

body, O. H. N. are eminently mobile, elastic, and possess great atomic heat. 

C. H. N. are distinguished for the narrow range and feebleness of their 

affinities and chemical inertia. C. has the greatest atomic cohesion. O. 

is noted for the number and intensity of its combinations, and its remark- 
able display of chemical activity. 

Chemical elements do not exist alone in the body, but are combined in 

characteristic proportions to form comipounds,thQ proximate principles, which 

are the ultimate compounds to which the fluids and solids can be reduced, 
Proximate principles exist in the body under their own form, and can 

be extracted without losing their distinctive properties. 



CHEMICAL COMPOSITION OF THE BODY. 11 

There are about one hundred proximate principles, which are divided 
into four classes, viz : inorganic, organic non-nitrogenized, organic nitro- 
genized, and principles of waste. 

I. INORGANIC PROXIMATE PRINCIPLES. 

SUBSTANCE. WHERE FOUND. 

Oxygen Lungs and blood. 

Hydrogen Stomach and intestines. 

Nitrogen Blood and intestines. 

Carbonic anhydride Expired air of lungs. 

Carburetted hydrogen 1 T -, . , ,. 

J te V Lungs and intestines. 

Sulphuretted hydrogen J 

Water Found in all solids and fluids. 

Sodium chloride In all fluids and solids except enamel . 

Potassium chloride In muscles, liver, saliva, gastric juice, etc. 

Ammonium chloride Gastric juice, saliva, tears, urine. 

Calcium chloride Bones, teeth, urine. 

Calcium carbonate Bones, teeth, cartilage, internal ear, blood. 

Calcium phosphate 



In all fluids and solids of the body. 



Magnesium phosphate 
Sodium phosphate 
Potassium phosphsite 

Sodium sulphate } TT . -, .,, , ., , .. . . . 

r > Universal, except milk, bile and gastric juice. 

Potassium sulphate J 

Sodium carbonate ") ^ , , , , 

V Blood, bones, lymph, urine, etc. 

Potassium carbonate J 

Sodium carbonate Blood. 

Magnesium carbonate Blood and sebaceous matter. 

Inorganic principles enter and leave the body under their own form. 

Water gives elasticity to the tissues, and is a general solvent. Sodium 

chloride regulates osmotic action (exudation and absorption), influences 

the form and consistence of blood corpuscles. Calcium phosphate gives 

solidity and resistance to bones. 

II. ORGANIC NON-NITROGENIZED PRINCIPLES. 

FATS. C. O. H. 

Palmitin, -| Palmitic acid, ^ 

Stearin, v Neutral Fats. Stearic acid, V Fatty Acids. 

Olein, J Oleic acid, J 

The neutral fats, when combined in proper proportions, constitute a 
large part of the fatty tissue of the body ; they are soluble .in ether, chloro- 



12 HUMAN PHYSIOLOGY. 

form and hot alcohol ; insoluble in cold alcohol and water, and liquefy at a 
high temperature ; by boiling with a caustic alkali they are decomposed 
into glycerine and fatty acids. 

The fatty acids combined with sodium, potassium and calcium, are found 
as salts in various fluids of the body, such as blood, chyle, fseces, etc. 
Phosphorized fats in nervous tissue, butyric acid in milk, propionic acid in 
sweat, are also constituents of the body. 

Fat is derived from the food, stored up in the form of vesicles in and 
around the various anatomical structures and beneath the skin, constitut- 
ing the adipose tissue ; it serves as a non-conductor of heat, and gives 
roundness and form to the body. During the process of nutrition fat 
undergoes oxidation, attended by the evolution of heat and the manifesta- 
tion of muscular and nervous force. 

sugars, c. o. H. 

Glycogen, or Amyloid substance. 

Lactose, or Milk sugar. 

Dextrose, or Grape sugar. 

Inosite, or Muscle sugar. 

Dextrine. 
Sugar is found in many of the tissues and fluids of the body, e. g., liver, 
placenta, blood, milk, muscles, etc. The varieties of sugar are soluble in 
water, assume the crystalline form upon evaporation, and are converted 
into alcohol and carbonic anhydride by fermentation. Sugar is derived 
from the food, absorbed into the blood, where it largely disappears, under- 
going a transformation into fat ; or it is directly oxidized, thus contributing, 
like the fats, to the production of heat and force. 

III. ORGANIC NITROGENIZED PRINCIPLES. 





ALBUMENS. C. O. H. N. S. P. 




Albumen. 


Myosin. 


Mucin. 


Albuminose. 


Protagon. 


Chondrin. 


Fibrin. 


Pepsin. 


Elastin. 


Casein. 


Pancreatin. 


Keratin. 


Ostein. 


Salivin. 


Globulin. 



The albuminous co?7ipounds are organic in their origin, being derived 
from the animal and vegetable world ; they are taken into the body as 
food, appropriated by the tissues constituting their organic basis ; they dif- 
fer from the non-nitrogenized substances in not being crystalline, but 
amorphous, in having a less definite but more complex composition, and 
containing in addition to C. O. H., nitrogen, with, at times, sulphur and 



CHEMICAL COMPOSITION OF THE BODY. 13 

phosphorus. The albumens possess characteristics which distinguish them 
from all other substances : viz., a molecular mobility, which permits 
isomeric modifications to take place with great facility. 

Under favorable conditions they promote chemical changes, by their 
presence [catalysis] in other substances : e. g., during digestion, salivin 
and pepsin cause starch and albumen to be transformed into sugar and 
albuminose respectively. Different albumens possess varying propor- 
tions of water, which they lose when subjected to desiccation, becoming 
solid ; but upon exposure to moisture they again absorb water, regaining 
their original condition — they are hygroscopic. Another property is that of 
coagulation, which takes place under certain conditions : e.g., the presence 
of mineral acids, heat, alcohol, etc. 

After death the albuminous compounds undergo putrefactive changes, 
giving rise to carburetted and sulphuretted hydrogen and other gases. 

Albumen exists in the blood, lymph, chyle, constituting the pabulum of 
the tissues ; it is coagulated by heat, mineral acids, and alcohol. 

Peptones are formed in the stomach from the digestion of albuminous 
principles of the food ; they are coagulated by tannic acid, chlorine, 
acetate of lead, and characterized by great diffusibility, permitting them to 
pass through animal membranes with facility. 

Fibrin can be obtained from freshly drawn blood by whipping ; it also 
coagulates spontaneously, and when examined microscopically exhibits a 
filamentous structure. 

Casein is the albuminous principle of milk. 

Ostein constitutes the organic basis of bone, with which are mingled the 
salts of lime. 

Myosin is found in muscles, protagon in brain, pepsin, pancreatin and 
salivin, in the- digestive fluids. 

Mucin, chondrin, elastin, keratin, and globulin, are found in mucus, 
cartilage, elastic tissues, hair, nails, and red corpuscles, respectively. 

As the properties of the compounds formed by the union of elements 
are the resultants of the properties of the elements themselves, it follows 
that the ternary substances, sugars, starches and fats, possess a great 
inertia and a notable instability ; while in the more complex albuminous 
compounds, in which sulphur and phosphorus are united to the four chief 
elements, molecular mobility, resulting in isomerism, exists in a high 
degree. As these compounds are unstable, of a great molecular mobility, 
they are well fitted to take part in the composition of organic bodies, in 
which there is a continual movement of composition and decomposition. 



14 



HUMAN PHYSIOLOGY. 



Urates. 



IV. PRINCIPLES OF WASTE. 

Urea. Xanthin. Sodium, 

Creatin. Tyrosin. Potassium, 

Creatinin. Hippuric Acid. Ammoniuirij 

Cholesterin. Calcium Oxalate. Calcium, J 

These principles which represent waste, are of organic origin, arising 
within the body as products of disassimilation or retrograde metamorphosis 
of the tissues ; they are absorbed by the blood, carried to the various excre- 
tory organs, and by them eliminated from the body. 

The excrementitious substances will be fully considered under excre- 
tion. 

Proximate Quantity of the Chemical Elements and Proximate 
Principles of Body Weighing 154 lbs. 



lbs. 

Oxygen 11 1 

Hydrogen 14 

Nitrogen 3 

Carbon 21 

Calcium 2 

Phosphorus 1. 

Sodium, etc 



12 
12 



lbs. 
Water in 

Albuminoids 23 

Fats 12 

Calcium phosphate.... 5 
Calcium carbonate.... I 

Calcium fluoride 

Sodium sulphate, etc. 



13 

3 
9 



154 



154 



STRUCTURAL COMPOSITION of THE BODY. 

The study of the structure of the body reveals that it is composed of 
dissimilar parts, e. g., bones, muscles, nerves, lungs, etc. ; while these, 
again, by closer examination, can be resolved into elementary structures, 
the tissues, e. g., connective tissue, muscular, nervous, epithelial tissue, etc. 

Microscopical examination of the tissues shows that they are com- 
posed of fundamental structural elements, termed cells. 

Cells are living physiological units ; the simplest structural forms 
capable of manifesting the phenomena of life. 

A cell consists of a cell wall, cell contents and a nucleus. They vary in 
size from the -g-oV^h to tne -g-^o'th of an inch in diameter; when young 
and free to move in a fluid medium they assume the spherical form; 
but when subjected to pressure, may become flattened, cylindrical, fusiform 
or stellate. 

Structure of cells. The cell membrane is not an essential structure, as 
many cells are entirely devoid of it. When present it may exist as a thin, 



STRUCTURAL COMPOSITION OF THE BODY. 15 

transparent membrane, permeable to fluids, or merely as a thickening of 
the periphery of the cell contents. 

The cell substance in young cells is a soft, viscid, albuminous matter, 
unstable, insoluble in water, known as protoplasm, bioplasm, sarcode, etc. ; 
in older cells the original cell substance ^undergoes various transforma- 
tions, and is partly replaced by fat globules, pigment and crystals. 

The nucleus is a small vesicular body in the interior of the cell sub- 
stance, and frequently contains smaller bodies, the nucleoli. 
MANIFESTATIONS OF CELL LIFE. 

Growth. Cells when newly formed are exceedingly small, but as they 
approach maturity they increase in size, by the capability which the cells 
possess of selecting and appropriating new material as food, vitalizing and 
organizing it. The extent of cell growth varies in different tissues ; in 
some they remain exceedingly small, in others they attain considerable 
size. In many instances the matter of which a cell is composed' undergoes 
transformation into new compounds destined for some ulterior purpose. 

Reproduction. Like all organic structures cells have a limited period of 
life ; their continual decay and death necessitates a capability of reproduc- 
tion. Cells reproduce themselves in the higher animals mainly hy fission. 
This is seen in the white blood corpuscles of the young embryos of ani- 
mals ; the corpuscle consists of a cell substance and nucleus. When 
division of the cell is about to take place, the nucleus elongates, the cell 
substance assumes the oval form, a constriction occurs, which gradually 
deepens, until the original cell is completely divided and two new cells are 
formed, each of which soon grow to the size of the parent cell. 

In cells provided with a cell membrane the process is somewhat different. 
In the ova of the inferior animals, after fertilization has taken place, a 
furrow appears on the opposite sides of the cell substance, which 
deepens until the cell is divided into two equal halves, each containing a 
nucleus ; this process is again repeated until there are four cells ; then 
eight, and so on until the entire cell substance is divided into a mulberry 
mass of cells, completely occupying the interior of the cell membrane. 
The whole process of segmentation takes place with great rapidity, occupy- 
ing not more than a few minutes, in all probability. 

Motion. Spontaneous movement has been observed in many of the 
cells of the body. It may be studied, for example, in the movements of 
the spermatozoa, the waving of the cilia covering the cells of the bronchial 
mucous membrane, the white corpuscles of the blood, etc. 



16 HUMAN PHYSIOLOGY. 

By a combination and transformation of these original structural ele- 
ments, and material derived from them, all the tissues are formed which 
enter into the structure of the human body. 

CLASSIFICATION OF TISSUES. - 

I. Homogeneous Substance, a more or less solid, albuminous, struc- 
ture, filling the spaces between the cells and fibres of various tissues, e. g., 
cartilage, bone, dentine, etc. 

II. Limiting Membrane, a thin, homogeneous membrane, structure- 
less, composed of coagulated albumen, and often not more than the' 
's'olTootk °f an i ncn in thickness, found lining the blood vessels and 
lymphatics, forming the basement membrane of the skin and mucous 
membranes, the posterior layer of the cornea, the capsule of the crystalline 
lens, etc. 

III. Simple fibrous or filamentous tissue — the elements of which 
are real or apparent filaments. 

(a) Connective or areolar; white fibrous tissue ; constituting tendons, 
ligaments, aponeuroses, periosteum, dura mater, synovial membranes, vas- 
cular tunics, etc. 

(b) Yellow elastic tissue, found in the middle coats of arteries, veins, 
lymphatics, ligamentum nuchse,. vocal cords, ligamenta subflava, etc. 

IV. Compound membranes (membrano-cellular or fibro-cellular 
tissues), cells aggregated into laminae. 

(a) Epidermic tissue; (b) epithelial tissue ; (c) glandular tissue; 
(d) cornea. 

V. Cells containing coloring matter, or pigment cells, e. g., skin, 
choroid membrane, etc. 

VI. Cells coalesced or consolidated by internal deposits, e. g., 
hair, nails, bone, teeth, etc. 

VII. Cells imbedded in an intercellular substance, e. g., cartilage, 
crystalline lens, etc. 

VIII. Cells aggregated in clusters, forming tissues more or less 
solid, e. g., adipose tissue, lymphatic glands. 

IX. Cells imbedded in a matrix of capillaries, e. g., grey or vesicular 
nervous matter. 

X. Cells whose coalesced cavities form tubes containing liquids or 
secondary solid deposits, e. g., vascular tissue, dentine. 

XI. Cells free, isolated or floating— fluid tissue — e. g., red and white 
blood corpuscles, lymph and chyle corpuscles. 



FOOD. 17 

FOOD. 

A Food may be defined to be any substance capable of playing a part 
in the nutrition of the body. 

Food is required to repair the waste of the tissues consequent on their 
functional activity, and for the generation of force. 

Hunger and Thirst are sensations which indicate the necessity for 
taking food ; they arise in the tissues at large, and are referred to the 
stomach and fauces, respectively, through the sympathetic nervous system. 

Inanition or Starvation results from insufficiency or absence of food ; 
the phenomena of which are hunger, insatiable thirst, pain referred to the 
epigastrium, weakness and emaciation; a foetid odor exhaled from the 
oody, showing a tendency to decomposition ; stupor, followed by delirium ; 
fall of temperature ; and death from exhaustion, and, at times, convulsions. 

During starvation the loss of different tissues, before death occurs, aver- 
ages T %ths, or 40 per cent, of their weight. 

Those tissues which lose more than 40 per cent, are fat, 93.3, blood, 75, 
spleen, 71.4, pancreas, 64.1, liver, 52, heart, 44.8, intestines, 42.4, mus- 
cles, 42.3. Those which lose less than 40 per cent, are muscular coat of 
stomach, 39.7, pharynx and oesophagus, 34.2, skin, 33.3, kidneys, 31.9, 
respiratory apparatus, 22.2, bones, 16.7, eyes, 10, nervous system, 1.9. 

The fat almost entirely disappears, except a small quantity in the pos- 
terior portion of the orbits and around the kidneys. 

The appearances presented by the body after death from starvation 
are those of anaemia and great emaciation; bloodlessness ; absence of fat; 
stomach and bowels empty, the coats of which are thin and transparent ; 
decomposition of the body readily takes place. 

The duration of life after complete deprivation of food varies from eight 
to thirteen days, though life may be prolonged if a small quantity of water 
be obtained. 

CLASSIFICATION OF ALIMENTARY PRINCIPLES. 

1. Albuminous group — nitrogenized, C. O. H. N. S. P. 

PRINCIPLE. WHERE FOUND. 

Myosin, syntonin Flesh of animals. 

Vitellin, albu?nen Yolk of egg, white of Qgg. 

Fibrin, globulin Blood contained in meat. 

Casein Milk, cheese. 

Gluten ....Grain of wheat and other cereals. 

Vegetable albumen Soft growing vegetables. 

Legumin Peas, beans, lentils, etc. 

Gelatin Bones. 



18 HUMAN PHYSIOLOGY. 

2. Saccharine group — non-nitrogenized, C. O. H. 

Cane sugar, beet root sugar .. Sugar cane, beets, etc. 

Glucose, grape sugar Fruits. 

Inosite, liver stigar, glycogen Muscles, liver, etc . 

Lactose or milk sugar Milk. 

Starch,,., , , Cereals, tuberous roots and legu- 
minous plants. 

3. Oleaginous group — non-nitrogenized, C. O. H. 

Animal fats and oils ... 1 Found in the adipose tissue of 

Stearin, olein f- animals, seeds, grains, nuts, fruits, 

Palmatin, fatty acids., j and other vegetable tissues. 

4. Inorganic group. Water, sodium and potassium chlorides, sodium, 
calcium, magnesium and potassium phosphates, calcium carbonate and 
iron. 

5. Vegetable acid group. Malic, citric, tartaric and other acids, 
found principally in fruits. 

6. Accessory foods. Tea, coffee, alcohol, cocoa, etc. 

The albuminous principles enter largely into the composition of the 
body, and constitute the organic bases of the different tissues; they are 
required for the growth and repair of the tissues, but when employed 
exclusively as food for any length of time are incapable of supporting life ; 
they give rise, to some extent, to the evolution of force ; but muscular 
work does not result from the oxidation of albuminous compounds. 

The saccharine principles are important to the process of nutrition, but 
the changes which they undergo are not fully understood ; they form but 
a small proportion of the animal tissues, and by oxidation generate heat 
and force. Starch undergoes conversion into dextrin and grape sugar. 

The oleaginous principles form a large part of the tissues of the body. 
They are introduced into the system as food, and are formed also from a 
transformation of saccharine and albuminous matter during nutrition ; they 
enter into the composition of nervous and muscular tissue, and are stored up 
as adipose tissue, giving roundness to the form and retaining heat ; finally 
undergoing oxidation attended by the production of heat and the evolution 
of muscular and nervous force. 

The inorganic principles constitute an essential part of all animal tissues, 
and are introduced with the food. 

Water is present in all fluids and solids of the body, holding their 
ingredients in solution, promoting the absorption of new material into 
the blood and tissues, and the removal of waste ingredients. 



FOOD. 19 

Sodium chloride is an essential constituent of all tissues, regulating the 
passage of fluids through animal membranes (endosmosis and exosmosis.) 

Calcium phosphate gives solidity to bones and teeth, constituting more 
than one-half their substance. 

Iron is a constituent of the coloring matter of the blood. 

The vegetable acids are important to nutrition, and tend to prevent the 
scorbutic diathesis. 

The accessory foods also influence the process of nutrition. Tea excites 
the respiratory function, increasing the evolution of carbonic acid. Coffee 
is a stimulant to the nervous system ; increases the force of the heart's 
action and retards waste. Alcohol diminishes the elimination of urea and 
carbonic acid, lowers the temperature, does not generate force, acts as a 
temporary stimulant, is useful in exhaustion, enfeebled digestion and other 
pathological conditions. 

A proper combination of different alimentary principles is essential 
for healthy nutrition ; no one class being capable of maintaining life for 
any definite length of time. 

An excess of albuminous food promotes the arthritic diathesis, manifest- 
ing itself as gout, gravel, etc. 

An excess of oleaginous food gives rise to the bilious diathesis, while a 
deficiency of it promotes the scrofulous. 

Farinaceous food when long continued in excess, favors the rheumatic 
diathesis by the development of lactic acid. 

The Alimentary Principles are not introduced into the body as such, 
but are combined in proper proportions to form compound substances, 
termed foods, e. g., bread, milk, eggs, meat, etc., the nutritive value of 
each depending upon the extent to which these principles exist. 

. PERCENTAGE COMPOSITION OF DIFFERENT FOODS. 

WATER. ALBUMEN. STARCH. SUGAR. FATS. SALTS. 

Bread 37 8.1 47.4 3.6 1.6 2.3 

Milk 86 4.1 ... 5.2 3.9 0.8 

Eggs 74 14.0 ... ... 10.5 1.5 

Meat 54 27.6 ... ... 15.45 2.95 

Potatoes 75 2.1 18.8 3.2 0.2 0.7 

Corn 14 n. 1 64.7 0.4 8.1 1.7 

Oatmeal 15 12.6 58.4 5.4 5.6- 3 

Turnips 91 1.2 5.1 2.1 ... 6 

Carrots 83 1.3 8.4 6.1 0.2 1.0 



20 HUMAN PHYSIOLOGY. 

The .amount of food required in 24 hours has been estimated at about 
5^ pounds, comprising meat, 16 oz. ; bread, 19 oz. ; fat, 3% oz - '> water, 
52 fluid oz. 

In the excreta of the body the normal proportion of N. to C. is i to 15. 
To maintain this relation, a proper proportion of nitrogenized to non-nitro- 
genized articles should be observed in diet. Meat, J^ft), and bread, 2* 
lbs, would furnish the necessary amount of N. and C, thus compensating 
for the loss. 

COMPARISON OF INGESTA AND EGESTA IN 24 HOURS. 

FOOD, DRINK, AIR. OZ. EXCRETIONS. OZ. 

Albumen 4.2^. -r, ,, f carbonic acid 1 

^ ° Breathe , v 43 -40 

Starch 11.63. \ watery vapor j T* * 

Fats..., ;. 3.17. 

Salts 1. 1 3. 

Water (6 pints). 93.00; Urine 66.31 



,-> . , . f carbonic acid ) , 

Perspiration < y 23.02 

r ( watery vapor J ° 

Urine 66.31 

Oxygen., 26.24. Solid excreta 6.07 



Total 139.40. Total I39-4-0 

DIGESTION. 

Digestion is a physical and chemical process, by which the food is 
changed by the action of solvent fluids into a form capable of being ab- 
sorbed into the blood. 

The Digestive Apparatus consists of the alimentary canal and its ap- 
pendages, viz : teeth, salivary, gastric and intestinal glands, liver and 
pancreas. 

Digestion may be divided into seven stages : prehension, mastication, 
insaiivation, deglutition, gastric and intestinal digestion and defecation. 

Prehension is the act of conveying food into the mouth, accomplished 
by the hands, lips, and teeth. 

By the Act of Mastication the food is thoroughly triturated, so as to 
present a greater surface for the action of the digestive fluids ; it is accom- 
plished by the teeth and lower jaw, under the influence of muscular con- 
traction. 

The Teeth are thirty-two in number, sixteen in each jaw, and divided into 
four incisors or cutting teeth, two canines, four bicuspids, and six molars 
or grinding teeth ; each tooth consists of a crown covered by enamel, a 
neck, and a root surrounded by the crusta petrosa, and imbedded in the 
alveolar process ; a section through a tooth shows that its substance is 



DIGESTION. 21 

made up of dentine, in the centre of which is the pulp cavity, containing 
blood vessels and nerves. 

The lower jaw is capable of making a downward and an upward, a 
lateral and an antero-posterior movement, dependent upon the construc- 
tion of the temporo-maxillary articulation. 

The jaw is depressed by the contraction of the digastric, genio-hyoid, 
mylo-hoid and platysma myoidesn\\±$>o\^\ elevated 'by the temporal, masseter 
and internal pterygoid muscles ; moved laterally by the external pterygoids 
contracting alternately. 

The food is kept between the teeth by the intrinsic and extrinsic mus- 
cles of the tongue from within, and the orbicularis oris and buccinator 
muscles from without. 

The Movements of Mastication are called forth by reflex action 

through the medulla oblongata, induced by the presence of food in the 

mouth. 

NERVOUS CIRCLE OF MASTICATION. 

AFFERENT OR EXCITOR NERVES. EFFERENT OR MOTOR. 

1. Lingual branch of 5th pair. 1. 3d branch of 5th pair. 

2. Glossopharyngeal. 2. Hypo-glossal, 

3. Facial. 

Insalivation is the incorporation of the food with the saliva, secreted 
by the parotid, sub '-maxillary and sub- lingual glands ; the parotid saliva, 
thin and watery, is poured into the mouth through Steno's duct ; the sub- 
maxillary and sub-lingual salivas, thick and viscid, are poured into the 
mouth through Wharton's and Bartholini's ducts. 

Saliva is an opalescent, slightly viscid, alkaline fluid, having a sp. gr. of 
1.005. The quantity secreted in 24 hours is rather less than three pounds. 

It is composed of water, organic matter [ptyalin) and inorganic salts. 

Its function is twofold — 

1 . Physical. Softens and moistens the food, glues it together, and facili- 
tates swallowing. 

2. Chemical. Due to the presence of the organic ferment, ptyalin, 
converting starch into sugar. 

The secretion of saliva is regulated by nervous influence. 
NERVOUS CIRCLE OF INSALIVATION. 

AFFERENT OR EXCITOR NERVES. EFFERENT OR MOTOR. 

1. Lingual branch of 5th pair I. Auricula-temporal (branch of 5th 

2. Glosso-pharyngeal. pair for parotid gland.) 

2. Chorda-tympani, for sub-maxillary 
and sub-lingual glands. 



22 HUMAN PHYSIOLOGY. 

Deglutition is the act of transferring food from the mouth into the 
stomach, and may be divided into three. stages : — 

1. The passage of the bolus from the mouth into the pharynx. 

2. From the pharynx into the oesophagus. 

3. From the oesophagus into the stomach. 

In the 1st stage, which is entirely voluntary, the mouth is closed and 
respiration momentarily suspended ; the tongue, placed against the roof of 
the mouth, arches upward and backward, and forces the bolus into the fauces. 

In the 2d stage, which is entirely reflex, the palate is made tense and 
directed obliquely backward ; the bolus is grasped by the superior con- 
strictor muscle of the pharynx and rapidly forced into the oesophagus. 

The food is prevented from entering the posterior nares by the uvula 
and the closure of the posterior half-arches (the palato-pharyngei muscles); 
from entering the larynx by its ascent under the base of the tongue and 
the action of the epiglottis. 

In the jd stage, the longitudinal and -circular muscular fibres, contracting 
from above downward, strip the bolus into the stomach. 

Gastric Digestion. The stomach is a dilatation of the alimentary 
canal, 13 inches long, 5 inches deep, having a capacity of about 5 pints; 
there can be distinguished a cardiac and pyloric orifice, a greater and lesser 
curvature, a greater and lesser pouch. 

It possesses three coats :- — 

1. Serous, a reflection of the peritoneum. 

2. Muscular, the fibres of which are arranged longitudinally, transversely 
and obliquely. 

3. Mucous, thrown into folds forming the rugae ; imbedded in the 
mucous coat are immense numbers of mucous and true gastric glands; the 
former, found in the pyloric portion, are lined by columnar epithelium 
throughout their depth ; the latter, found in the cardiac end, mainly con- 
tain oval, spherical cells, granular, and nucleated ; the true peptic cells. 

In the Stomach the food is disintegrated and dissolved by incorpora- 
tion with the gastric juice secreted by the gastric glands. 

Gastric Juice is a clear, straw-colored fluid, decidedly acid, with a 

specific gravity of 1.005 t0 i-oio.. 

COMPOSITION OF GASTRIC JUICE. 
Water 975 .00 

Free acid (hydrochloric) (?) 4.78 

Pepsin , 15.00 

Inorganic salts 5.22 

1000.00 



DIGESTION. „ 23 

The amount of gastric juice secreted in 24 hours varies under normal 
conditions from 8 to 14 pounds. 

Pepsin is an organic, nitrogenous ferment ; and the digestive action of 
gastric juice is due to its presence in combination with hydrochloric acid. 

The principle action of gastric juice is to convert the albuminoid 
substances of the food into albuminose or peptones, which differ from albu- 
men in being — 

1 . Diffusible, passing rapidly through the animal membranes, and being 
easily absorbed. 

2. Are not coagulated by heat, acetic or nitric acids, but can be precipi- 
tated by tannic acid. 

3. Soluble in water and saline solutions. 

Gastric Digestion occupies from 3 to 5 hours on the average ; varies 
according to the nature of the food, the quantity, exercise, etc. 

Movements of the Stomach. As soon as digestion commences, the 
cardiac and pyloric orifices are closed ; the walls of the stomach contract 
upon the food, and a peristaltic action begins, which carries the food 
along the greater and lesser curvatures, and thoroughly incorporates it 
with the gastric juice. As soon as any portion of the food is digested it 
passes through the pylorus into the intestine. 

Intestinal Digestion. The intestine is about 20 feet long, iy^ inches 
in diameter, and possesses three coats. 

1. Serous (peritoneal). 

2. Muscular, the fibres of which are arranged longitudinally and trans- 
versely. 

3. Mucous, thrown into folds, forming the valvulce conniventes. 

This stage of digestion is probably the most complex and important ; 
here the different alimentary principles are further elaborated and prepared 
for absorption into the blood by being acted upon by the intestinal juices, 
pancreatic juice and bile. 

Throughout the mucous coat are imbedded the intestinal follicles, the 
glands of Brunner and Lieberkuhn. 

They secrete the true intestinal juice, which is an alkaline, viscid fluid, 
composed of water, organic matter and salts. Its function is to convert 
starch into glucose, and assist in the digestion of the albuminoids. 

Pancreatic Juice is secreted by the pancreas, a flattened gland about 
six inches long, running transversely across the posterior wall of the abdo- 
men, behind the stomach ; its duct opens into the duodenum. 

The pancreatic fluid is transparent, colorless, strongly alkaline and 
viscid, having a specific gravity of 1.040. 



24 HUMAN PHYSIOLOGY. 

COMPOSITION OF PANCREATIC JUICE. 

Water 900.76 

Pancreatin . , 90.44 

Inorganic salts 8.80 

1000.00 
The pancreatin is the most important constituent, and gives to the fluid 
its digestive power. Coagulated by heat, nitric acid and alcohol. 
The functions of the pancreatic fluid are — 

1 . To transform starch and cane sugar into glucose. 

2. To emulsify the oils and fats, and split them up into fatty acids and 
glycerine. 

3. To convert albuminoid substances into peptones. « 
The emulsification of the fats seems to be the principal office of the pan- 
creatic juice; disease of the pancreas, preventing the . discharge of its 
secretion into the intestine, is attended by an abundant discharge of fat from 
the bowels. 

The total quantity of this fluid secreted in 24 hours has not been accu- 
rately determined ; varies from one to two pounds. 

Bile has an important influence in the elaboration of the food and its 
preparation for absorption. It is a golden-brown, viscid fluid, having a 
neutral or slightly alkaline reaction and a specific gravity of 1.020. 
COMPOSITION OF BILE. 

Water 859.2 

Sodium glycocholate \ 
Sodium taurocholate / 

Fat 9.2 

Cholesterine 2.6 

Mucus and coloring matter 29.8 

Salts 7.8 

1 000.0 

The biliary salts are characteristic ingredients, and are formed in the 
liver by the process of secretion, from materials furnished by the blood. 
They probably aid digestion. 

Cholesterine is a product of waste taken up by the blood from the tissues 
and excreted by the liver. 

The coloring matters which give the tints to the bile are biliverdin and 
bilirubin, and are probably derived from the coloring matter of the blood. 



ABSORPTION. 25 

The bile is both a secretion arid an excretion; it is constantly being 
formed and discharged by the hepatic ducts into the gall bladder, inwhich 
it is stored up, during the intervals of digestion. As soon as food enters 
the intestines, it is poured out abundantly by the contraction of the walls 
of the gall bladder. 

The amount secreted in 24 hours is about 2^ pounds. 

Functions of the bile. It assists in the emulsification of the fats and 
promotes their absorption. 

It tends to prevent putrefactive changes in the food. 

Stimulates the secretions of the intestinal glands, and excites the normal 
peristaltic movements of the bowels. 

The digested food, the chy?ne,\s a grayish, pultaceous mass, but as it 
passes through the intestines it becomes yellow, from admixture with the 
bile. It is propelled onward by vermicular motion ; by the contraction of 
the circular and longitudinal muscular fibres. 

As the digested food passes through the intestines the nutritious matters 
are absorbed into the blood, and the residue enters the large intestine. 

The Faeces consist chiefly of indigestible matters, excretin, stercorin, 
and salts ; varying in amount from 4 to 7 oz. in 24 hours. 

Defecation is the voluntary act of extruding the faeces from the body ; 
accomplished by a relaxation of the sphincter muscle, the contraction of 
the walls of the rectum, assisted by the abdominal muscles. 

The gases contained in the stomach and small intestine are oxygen, 
nitrogen, hydrogen, and carbonic acid. In the large intestine, carbonic 
acid, sulphuretted and carburetted hydrogen. They are introduced with 
the food, and also developed by chemical changes in the alimentary canal. 
They distend the intestines, aid capillary circulation, and tend to prevent 
pressure. 

ABSORPTION. 

Absorption has for its object the introduction of new materials into the 
blood, and takes place mainly from the alimentary tract ; but also to some 
extent from the skin, respiratory surface and closed cavities of the body. 

The agents of absorption are the veins and lymphatics. 

As a result of the process of digestion the different alimentary substances 
are converted into forms which are capable of being absorbed into the 
blood, e. g., albuminose, glucose and fatty emulsion. Water and inorganic 
matters undergoing no change, being already in a condition to be ab- 
sorbed and to play a part in the nutritive process. 

The blood vessels which are most active as absorbents, are the gastric 



26 HUMAN PHYSIOLOGY. 

superior and inferior ?nesenieric veins. They arise in the coats of the ali- 
mentary canal, and as they converge, unite with the splenic vein to form the 
portal vein, which enters the liver. 

As the digested mass of food, the chyme, passes through the alimentary 
canal a large portion of it disappears ; the veins absorb water, albuminose, 
glucose, and inorganic salts, and convey them directly into the liver ; the 
blood of the portal vein being especially rich in these substances. 

At times, after the ingestion of large quantities of oleaginous food, the 
blood vessels take up, in addition, a certain quantity of fatty matter, but 
this is not usually the case ; the fats being absorbed by special vessels, 
the ly?nphatics or lacteals. 

General Anatomy of the Lymphatic System. The lymphatics 
constitute a system of minute, delicate, transparent vessels, which, having 
their origin at the periphery of the body, pass forward toward the centre 
and empty into the veins at the base of the neck, by means of the thoracic 
duct. In their course they pass through small ovoid bodies, the lymphatic 
glands. 

Origin of Lymphatics. The lymphatic vessels commence by a fine 
capillary plexus, or in irregular lymph spaces, distributed over the surface 
and throughout the interior of the various tissues of the body. 

The lymphatics of the small intestine, the lacteals, arise within the 
villous processes which cover its inner surface throughout its entire extent. 

Each villus is formed by an elevation of the mucous membrane, covered 
externally by a layer of columnar epithelial cells; in the interior are found 
numerous blood vessels, non-striated muscular fibres, and the beginnings of 
the lacteal vessels. 

The structure of the larger vessels resembles that of the veins, consisting 
of three coats — 

1. External, composed of fibrous tissue and muscular fibres, arranged 
longitudinally. 

2. Middle, consisting of white fibrous and yellow elastic tissue, non- 
striated muscular fibres, arranged transversely. 

3. Internal, composed of an elastic membrane, lined by epithelial cells. 
Throughout their course are found numerous semi-lunar valves, looking 

toward the larger vessels, formed by a folding of the inner coat and 
strengthened by connective tissue. 

Lymphatic Glands consist of an external fibrous covering, from the 
inner surface of which partitions of fibrous tissue, the trabecules, pass into 
the substance of the gland, forming a stro7?ia or network, in the meshes of 
which are found the true lymph corpuscles. 



ABSORPTION. 27 

The lymphatics which enter the gland are called the afferent vessels ; 
those which leave it, the efferent vessels. 

The Thoracic Duct is the general trunk of the lymphatic system, into 
which the vessels of the lower extremities, of the abdominal organs, of the 
left side of the head and left arm empty their contents. It is about twenty 
inches in length ; arises in the abdomen, opposite the third lumbar verte- 
bra, by a dilatation, the receptaculum chyli ; ascends along the verte- 
bral column to the seventh cervical vertebra, and terminates in the veins at 
the junction of the internal jugular and subclavian on the left side. The 
lymphatics of the right side of the head, of the right arm and the right side 
of the thorax, terminate in the right thoracic duct, about one inch in length, 
which joins the venous system at the junction of the internal jugular and 
subclavian on the right side. 

Lymph is a clear, transparent fluid, slightly alkaline, of a saline taste, 
having a specific gravity of 1.022. It is found in the lymphatic vessels 
throughout the body. 

Lymph contains a number of corpuscles (the leucocytes) resembling the 
white corpuscles of the blood, which increase in number as it passes 
through the lymphatic glands. They are about 2TVot n °^ an mcn m diam- 
eter and somewhat granular; they are discharged into the blood, but their 
function is obscure. When withdrawn from the vessels lymph undergoes 
spontaneous coagulation, separating into serum and clot, as in the case of 
the blood. 

COMPOSITION OF LYMPH. 

DR. OWEN REES. 

Water 96.536 

Proteids (serum-albumen, fibrin, globulin) , 1-320 

Extractives (urea, sugar, cholesterine) 1.559 

Fatty matter a trace. 

Salts 0.585 

100.000 
Origin of Lymph. Lymph is undoubtedly a transudation from the 
capillary blood vessels, occurring during the process of nutrition, and is 
identical, for the most part, with the liquor sanguinis, or plasma. As new 
material is constantly exuded, the old is absorbed by the lymphatics, and 
returned again to the circulation. 

Excrementitious matters, as urea, cholesterine, etc., are also taken up 
from the tissues by the lymphatics and emptied into the blood. 

The total quantity of lymph poured into the thoracic duct in 24 hours 
has been estimated at 3^ lbs. 



28 HUMAN PHYSIOLOGY. 

Chyle. As a result of the process of digestion, the oleaginous matters 
which have been acted upon by the pancreatic juice and bile are trans- 
formed into a condition of emulsion, forming an opaque, milky fluid, 
termed chyle, which adheres to the folds of the mucous membrane and 
villi. 

The Molecules of the fat are first absorbed by the epithelial cells upon 
the surface of the villi, through which they pass and enter the lymphatics. 
Absorption by the Lacteals. The lacteals, or lymphatics of the small 
intestine, have their origin in the interior of the villi, from which they 
emerge and form a lymphatic plexus ; the larger branches of which pass 
through the layers of the mesentery, and finally terminate in the thoracic 
duct. 

In the intervals of digestion the lacteals contain clear, transparent lymph, 
and are invisible, on account of their small size and delicacy. But during 
digestion these vessels become filled, from absorption of the chyle, and form 
a visible network of white vessels ramifying through the mesentery, and 
converging toward the receptaculum chyli. 

The lacteal vessels also absorb a small quantity of water, albuminose, 
glucose a?td salts. 

COMPOSITION OF CHYLE. 

Water e 902.37 

Albumen..... 35.16 

Fibrin 3.70 

Extractives 15.65 

Fatty matters.. 36.01 

Salts 7. 1 1 

1000.00 

The products of digestion find their way into the general circulation by 
two routes — 

1. Water, albuminose, glucose and salts, are mainly absorbed by the 
veins, carried into the liver, through the capillaries of which they pass, and 
enter the inferior vena cava by the hepatic veins. 

2. The fats are absorbed by the lacteals, emptied into the thoracic duct, 
and enter the blood at the junction of the internal jugular and subclavian 
veins. 

Forces aiding the movement of Lymph and Chyle. 
I . Endosmosis. The continued transudation of matter from the capil- 
laries, and its absorption into the lymphatics by endosmosis, constitutes the 



BLOOD. 29 

main cause, the vis-a-tergo, of the movement of the lymph; it is so con- 
siderable as to rupture the walls of the vessels if they are ligated. 

2. Contraction of the non-striated muscular fibres in the walls of the 
lymphatic vessels, especially when fully distended, aided by the action of 
the valves, promotes the onward flow of the fluids. 

3. Muscular contraction in all parts of the body, by exerting intermit- 
tent pressure upon the lymphatic vessels, hastens the current onwards ; 
regurgitation being prevented by the closure of the valves. 

4. The Inspiratory move?nent, by expanding the chest, causes a dilation 
of the thoracic duct, and a rapid flow of lymph and chyle into it ; during 
expiration it is compressed, and the "fluids forcibly expelled into the venous 
system. 

BLOOD. 

The Blood is a nutritive fluid containing all the elements necessary for 
the repair of the tissues ; it also contains principles of waste absorbed 
from the tissues, which are conveyed to the various excretory organs and 
by them eliminated from the body. 

The total amount of blood in the body is estimated to be about one- 
eighth of the body weight ; from 16 to 18 pounds in an individual of 
average physical development. The quantity varies during the 24 hours ; 
the maximum being reached in the afternoon, the minimum in the early 
morning hours. 

Blood is a heterogeneous, opaque red fluid, having an alkaline reaction, 
a saline taste and a specific gravity of 1.055. 

Opacity is due to the refraction of the rays of light by the elements of 
which the blood is composed. Color varies in hue, from a bright scarlet 
in the arteries to a deep purple in the veins, due to the presence of a color- 
ing matter, ' hcemoglobin in different degrees of oxidation. 

The alkalinity is constant, and depends upon the presence of the tri- 
sodium phosphate ; becomes acid in cholera and sunstroke. 

The saline taste is due to the amount of sodium chloride present. 

The specific gravity ranges within the limits of health from 1.045 to 
1.075. 

The odor of the blood is characteristic and varies with the animal from 
which it is drawn, due to the presence of caproic acid. 

The temperature ranges from 98 Fahr. at the surface to 107 Fahr. in 
. the hepatic vein ; it loses heat by radiation and evaporation as it approaches 
the extremities, and as it passes through the lungs. 



30 HUMAN PHYSIOLOGY. 

Blood consists of two portions : — 

1. The Liquor Sanguinis or Plasma, a transparent colorless fluid in 
which are floating— 

2. Red and white corpuscles ; these constituting by weight less than one 
half, 40 per cent., of the entire amount of blood. 

COMPOSITION OF PLASMA. 

DALTON. 

Water 902.00 

Albumen 53-°° 

Paraglobulin 2 2 .00 

Fibrinogen ,. 3 00 

Fatty matters 2.50 

Cry stallizable nitrogenous matters 4.00 v 

Other organic matter 5.00 

Mineral salts '. 8.50 



1000.00 

Water acts as a solvent for the inorganic matters and suspends the cor- 
puscular elements. 

Albumen is the nutritious principle of the blood ; it is absorbed by the 
tissues to repair their waste, and is transformed into the organic basis char- 
acteristic of each structure. 

Paraglobulin or jibrinoplastin is a soft amorphous substance precipitated 
by sodium chloride in excess or by passing a stream of carbonic acid 
through dilute serum. 

Fibrinogen can also be obtained by strongly diluting the serum and 
passing carbonic acid through it for a long time, when it is precipitated as 
a viscous deposit. 

Fatty matters exist in small proportion, except in pathological conditions 
and after the ingestion of food rich in oleaginous matters; it soon disap- 
pears, undergoing oxidation, generating heat and force, or is deposited as 
adipose tissue. 

Sugar is represented by glucose, a product of the digestion of saccharine 
matter and starches in the alimentary canal ; glycogenic matter is derived 
from the liver. 

The saline constituents aid the process of osmosis, give alkalinity to the 
blood, promote the absorption of carbonic acid from the tissues into the 
blood, and hold other substances in solution ; the most important are the 
sodium and potassium chlorides, the calcium and magnesium phosphates. 

Excrementitious matters are represented by carbonic acid, urea, creatin, 



BLOOD CORPUSCLES. 31 

creatinin, urates, oxalates, etc ; they are absorbed from the tissues by the 
blood and conveyed to the excretory organs, lungs, kidneys, etc. 

Gases. Oxygen, nitrogen, and carbonic acid exist in varying propor- 
tions. 

BLOOD CORPUSCLES. 

The blood corpuscles occur under two different forms, the red and the • 
white. The red corpuscles are circular biconcave disks, having an average 
diameter of the ^Vo^ °f an mcn » wnen viewed separately they are a pale 
straw color, but when massed together, present a dark red color. 

In man and the mammalia, the corpuscles present neither a nucleus 
nor a cell wall, and can be readily distinguished from the corpuscles of 
birds and reptiles, in which they are larger, are oval in shape, and contain 
a distinct nucleus. 

Blood corpuscles are exceedingly numerous, amounting to about 5,000,- 
000 in each cubic millimetre of blood (Vierordt, Welcker). 

The specific gravity is about 1.088. 

The red corpuscles consist of a firm, elastic, colorless framework, the 
stroma, in the meshes of which is entangled the coloring matter, the hoemo- 
g lob in. 

CHEMICAL COMPOSITION OF RED CORPUSCLES. 

Water.,. 688.00 

Globulin 282.22 

Haemoglobin IO -75 

Fatty matter , 2.31 

Extractives 2.60 

Mineral salts 8.12 



1000.00 

Hcemoglobin is an albuminous compound, composed of C. O. H. N. S. 
and iron ; it crystallizes in various forms ; unites readily with oxygen, giving 
to the resulting compound, oxy-hcemoglobin, a brilliant red color. 

A dilute solution of haemoglobin gives two absorption bands between 
the lines D and E of the solar spectrum. 

Hcematin results from the decomposition of haemoglobin. 

The function of the red corpuscles is to absorb oxygen and carry it to 
the tissues ; the smaller the corpuscles, and the greater the number, the 
more active are all the vital functions of the body. 

The white corpuscles are far less numerous than the red, the proportion 
being, on an average, about I white to 350 or 400 red ; they are globular 



32 HUMAN PHYSIOLOGY. 

in shape, and measure the -^J-^ g-th of an inch in diameter, consisting of a 
soft, granular, colorless substance, containing several nuclei. 

The white corpuscles possess the power of spontaneous movement, alter- 
nately contracting and expanding, throwing out processes of their substance 
and quickly withdrawing them, thus changing their shape from moment to 
moment. 

The white corpuscles are identical with the leucocytes, and are found in 
milk, lymph, chyle and other fluids. 

Their function is obscure. 

Origin of Corpuscles. The red corpuscles take their origin from the 
mesoblastic cells in the vascular area of the developing embryo. 

In the adult they are produced from colorless nucleated corpuscles, re- 
sembling the white corpuscles. The spleen is the organ in which they are 
finally destroyed. 

The white corpuscles originate from the leucocytes of the adenoid 
tissue, and subsequently give rise to the red corpuscles and partly to new 
tissues that result from inflammatory action. 

COAGULATION OF THE BLOOD. 

When blood is withdrawn from the body and allowed to remain at rest 
it becomes somewhat thick and viscid in from three to five minutes ; this 
viscidity gradually increases until the entire volume of blood assumes a 
jelly-like consistence, which occupies from five to fifteen minutes. 

The cause of this solidification is the appearance in the blood of 
fibrin; it exists in the proportion of three parts per thousand; it is 
soluble in water ; when examined microscopically shows a filamentous 
texture. 

As soon as coagulation is completed a second process begins, which con- 
sists in the contraction of the coagulum and the oozing of a clear, straw- 
colored liquid, the serum, from the meshes of the fibrin. The serum 
gradually increases in quantity as the clot diminishes in size, by contraction, 
until the separation is completed, which occupies from 12 to 24 hours. 
The changes in the blood are as follows : — 
Before coagulation. 

Liq. Sanguinis \ ("Water. 

or ( I Albumen, 

f Consisting of I -^ , » ,, 
Living blood, i Kasma J ] Paraglobulm. 



I Fibrinogen. 
[ Salts. 
Corpuscles. Red and white. 



COAGULATION OF THE BLOOD. 33 

After coagulation. 

f Crassamentum. >■_ ... (Fibrin. 

I _,_ _ ' t Containing ^ _ 

I Clot or coagulum. J (Corpuscles. 

Dead blood. J f Water. 

Serum, Containing J Albumen. 

j Paraglobulin. 
[ Salts. 

The buffy coat of the clot is due to the rapid sinking of the red corpus- 
cles beneath the surface, permitting the fibrin to coagulate without them, 
which then assumes a greyish-yellow tint ; continued contraction gives a 
cupped appearance to the surface of the clot. 

Inflammatory states of the blood produce a marked increase in the 
buffed and cupped condition, on account of the aggregation of the cor- 
puscles and their tendency to rapid sinking. 

Nature of Coagulation. Coagulable fibrin does not pre-exist in the 
blood, but is formed at the moment blood is withdrawn from the vessels. 
According to Denis, a liquid substance, plasmine, exists in the blood, which, 
when withdrawn from the circulation, decomposes into fibrin and met- 
albumen. 

According to Schmidt, fibrin results from the union of fibrinoplastin 
(paraglobulin) and fibrinogen, brought about by the presence of a third 
substance, the fibrin ferment. 

Conditions Influencing Coagulation. The process is retarded by 
cold, retention within living vessels, neutral salts in excess, inflammatory 
conditions of the system, imperfect aeration, exclusion from air, etc. 

It is hastened hy a temperature of ioo° F., contact with air, rough sur- 
faces and rest. 

Blood coagulates in the body after arrest of the circulation in the 
course of 12 to 24 hours; local arrest of the circulation from compression 
or a ligature, will cause coagulation, thus preventing hemorrhages from 
wounded vessels. 

The Composition of the Blood varies in different portions of the 
body. The arterial differs from the venous, in being more coagulable, in 
containing more oxygen and less carbonic acid, in having a bright scarlet 
color, from the union of oxygen with haemoglobin ; the purple hue of 
venous blood results from the deoxidation of the coloring matter. 

The blood of the portal vein differs in constitution, according to different 
stages of digestive process ; during digestion it is richer in water, albumin- 
ous matter and sugar ; occasionally contains fat ; corpuscles are dimin- 
ished, and there is an absence of biliary substances. 



34 HUMAN PHYSIOLOGY. 

The blood of the hepatic vein contains a larger proportion of red and 
white corpuscles ; the sugar is augmented, while albumen, fat and fibrin 
are diminished. 

Pathological conditions of the Blood. 

1. Plethora — increase in the volume or quantity of blood. 

2. Ancemia — deficiency of red globules with increase of water. 

3. Leucocyt hernia — increase of white and diminution of red corpuscles. 

4. Glycohoe?nia — excess of sugar in the blood. 

5. Urcemia — increase in the amount of urea. 

6. Cholestercemia — an excess of cholesterine in the blood. 

7. Thrombosis and embolism — clotting of blood in the vessels and dis- 
semination of coagula. 

8. Lipcemia — an excess of fat. 

9. Melancemia — pigment in the blood. 

CIRCULATION OF THE BLOOD. 

The Object of the Circulation is to distribute nutritious blood to all 
portions of the system and to carry waste materials to the various eliminat- 
ing organs. 

The Circulatory Apparatus consists of the heart, arteries, capillaries, 
and veins. 

The Heart is a hollow, muscular organ, pyramidal in shape, measuring 
5^ inches in length and weighing from 10 to 12 oz. in the male, and 8 to 
10 oz. in the female. It is invested externally by a fibro-serous closed sac, 
the pericardium, containing a small amount of fluid, which prevents friction 
as the visceral and parietal layers glide over each other, during the move- 
ments of the heart and lungs. 

The heart consists of four cavities, a right auricle and ventricle, and a 
left auricle and ventricle, completely separated by a vertical partition. The 
right is the venous side, receiving the blood from the venae cavse, and pro- 
pelling it through the pulmonary artery into the lungs ; the left is the arte- 
rial side, receiving the arterial blood from the lungs by the pulmonary veins, 
and propelling it through the aorta to the system at large. 

The auriculo-ventricular orifices are guarded on the right and left sides 
by the tricuspid and mitral valves respectively, while they are so arranged 
as to permit the flow of blood in the forward direction only; the orifices of 
the pulmonary artery and aorta are guarded by the semi-lunar valves. 

The endocardiu??i is a delicate, shining membrane lining the interior 
of the heart, and continuous with the lining membrane of the blood vessels. 

The walls of the left ventricle are nearly half an inch in diameter, being 



CIRCULATION OF THE BLOOD. 35 

two or three times thicker than the walls of the right; the force of its 
contraction being much greater. 

The Function of the Heart is to propel the blood to all portions of 
the vascular system ; accomplished by successive alternate contractions and 
relaxations of its muscular walls, constituting the systole and diastole. 

Course of the blood through the Heart. The venous blood re- 
turned to the heart by the superior and inferior venae cavae is emptied, 
during the diastole, into the right auricle, on the contraction of which it is 
forced through the right auriculo-ventricular opening into the right ventricle 
and distends it. Upon contraction of the ventricle the blood is propelled 
through the pulmonary artery into the lungs, where it undergoes aeration 
and is changed in color. 

The arterial blood is now collected by the pulmonary veins and poured 
into the left auricle; thence it passes into the left ventricle, which becomes 
fully distended. Upon the contraction of the ventricle, the blood is pro- 
pelled into the aorta, and by it distributed to the system at large, to be 
again returned to the heart by the veins. 

Regurgitation from the ventricles into the auricles during the systole is 
prevented by the closure of the tricuspid and mitral valves ; regurgitation 
from the pulmonary artery and aorta into the ventricles during the diastole 
is prevented by the closure of the semi-lunar valves. 

Movements of the Heart. At each revolution, during the systole, 
the heart hardens and becomes shortened in its long diameter ; its apex is 
raised up, rotated on its axis from left to right and thrown forward against 
the walls of the chest. The impulse of the heart is observed about two 
inches below the nipple, and one inch to the sternal side, between the fifth 
and sixth ribs, and caused mainly by the apex of the heart striking against 
the chest walls; assisted by the distention of the great vessels about the 
base of the heart. 

Sounds of the Heart. If. the ear be placed over the cardiac region 
two distinct sounds are heard during each revolution of the heart, closely 
following each other, and which differ in character. 

The sound coinciding with the systole in point of time, the first sound, is 
long and dull, and caused by the closure and vibration of the auriculo-ven- 
tricular valves, the contraction of the walls of the ventricles and the apex 
beat ; the second sound, occurring during the diastole, is short and sharp, 
and caused by the closure of the semi-lunar valves. 

The capacity of the left ventricle when fully distended is estimated at 
from four to seven ounces. 



36 HUMAN PHYSIOLOGY. 

The frequency of the heart's action varies at different periods of life, 
but in the adult male it beats about 72 times per minute. It is influenced 
by age, exercise, posture, digestion, etc. 

Age. Before birth the number of pulsations per minute averages 140 

During the first year diminishes to ,128 

During the third year diminishes to 95 

From the eighth to the fourteenth years averages 84 

In adult life the average is 72 

Exercise and digestion increase the frequency of the heart's action. 
Posture influences the number of pulsations per minute ; in the male, 
standing, the average is 81 ; sitting, 71 ; lying, 66; independent, for the 
most part, of muscular effort. 

The rhythmical movements of the heart are dependent upon, 1. An 
inherent irritability of the muscular fibres, which manifests itself as long as 
the nutrition is maintained. 2. The continuous flow of blood through its 
cavities distending them and stimulating the endocardium. 

The Nervous System regulates, to some extent, the cardiac movements. 

The pneumogastric nerves •, when galvanized, exert an inhibitory influ- 
ence over the heart, in virtue of their containing motor fibres derived from 
the spinal accessory ; division of these nerves increases the frequency of the 
heart's action. 

The sympathetic system, when galvanized in the neck, increases the num- 
ber of pulsations, and when divided they are decreased; the accelerator 
fibres coming from the medulla oblongata, enter the inferior cervical 
ganglion, and thence go to the heart. 

ARTERIES. 

The Arteries are a series of branching tubes conveying blood to all 
portions of the body. They are composed of three coats — 

1. External, formed of areolar and elastic tissue. 

2. Middle, contains both elastic and muscular fibres, arranged trans- 
versely to the long axis of the artery. The elastic tissue is more 
abundant in the larger vessels, the muscular in the smaller. 

3. Internal, composed of a thin homogeneous membrane, covered with 
a layer of elongated endothelial cells. 

The arteries possess both elasticity and contractility. 

The Property of Elasticity allows the arteries already full to accom- 
modate themselves to the incoming amount of blood, and to convert the 
intermittent acceleration of blood in the large vessels into a steady and 
continuous stream in the capillaries. 



ARTERIES. 37 

The contractility of the smaller vessels arrests hemorrhages, equalizes 
the current of blood, regulates the amount going to each part, and pro- 
motes the onward flow of blood. 

Blood pressure. Under the influence of the ventricular contraction and 
the recoil of the elastic walls of the arteries, the blood is constantly sub- 
jected to a certain amount of pressure ; which in the carotid artery of man 
is sufficient to support a column of mercury six inches high. To obtain 
the amount of pressure in any given artery, multiply the area of its trans- 
verse section by the height of the column of mercury supported by the 
carotid, taken as a standard. 

The blood pressure is influenced by 

1 . Ventricular systole. The more forcibly and the more frequently the 
heart contracts, the greater is the amount of blood pressure. 

2. Contraction of the smaller arteries impeding the flow of blood into the 
capillaries increases the pressure. 

3. Respiratory ??iove?nents. Inspiration diminishes the tension, expira- 
tion increases it. 

The pulse is the sudden distention of the artery, in a longitudinal and 
transverse direction. 

The Rate of Movement of the blood in the arteries varies ; being 
greatest in the larger .vessels, and during the ventricular systole, amounting 
in the carotid of the horse to 20 inches per second, and falling during the 
diastole to 9 inches. In ?nan the rapidity in the carotid has been esti- 
mated by Vierordt at 10 inches per second. 

The Calibre of the blood vessels is regulated by the vaso-motor 
nerves, which have their origin in the gray matter of the medulla oblongata. 
They issue from the spinal cord through the anterior roots of spinal nerves, 
pass through the sympathetic ganglia, and ultimately are distributed to the 
coats of the blood vessels. They exert, at different times, a constricting 
and dilating action upon the vessels, thus keeping up the arterial tonus. 

Capillaries. The capillaries constitute a network of vessels of micro- 
scopic size, which distribute the blood to the inmost recesses of the tissues, 
inosculating with the arteries on the one hand and the veins on the other ; 
they branch and communicate in every possible direction. 

The diameter of a capillary vessel varies from the Q-^-g-th to the j-jyg-g-th 
of an inch ; their walls consist of a delicate homogeneous membrane, the 
Tjo J-Q^th of an inch in thickness, lined by flattened, elongated, endothelial 
cells, between which, here and there, are observed sto?nata. 

It is through the agency of the capillary vessels that the phenomena of 



38 HUMAN PHYSIOLOGY. 

nutrition and secretion takes place, for here the blood flows in an equable 
aud continuous current, and is brought into intimate relationship with the 
tissues, two of the essential conditions for proper nutrition. 

The rate of movement in the capillary vessels is estimated at one inch 
in thirty seconds. 

In the capillary current the red corpuscles may be seen hurrying down 
the centre of the stream, while the white corpuscles in the still layer ad- 
here to the walls of the vessels ; and at times can be seen to pass through 
the walls of the vessel by amoeboid movements. 

The passage of the blood through the capillaries is mainly due to 
the force of the ventricular systole and the elasticity of the arteries ; but it 
is probably also aided by a power resident in the capillaries themselves, 
the result of a vital relation between the blood and the tissues. 

The Veins are the vessels which return the blood to the heart ; they 
have their origin in the venous radicles, and as they approach the heart, 
converge to form larger trunks, and terminate finally in the venae cava?. 

They possess three coats — 

1. External, made up of areolar tissue. 

2. Middle, composed of non-striated muscular fibres, yellow, elastic and 
fibrous tissue. 

3. Internal, an endothelial membrane, similar to that of the arteries. 
Veins are distinguished by the possession of valves throughout their 

course ; they are arranged in pairs, and formed by a reflection of the inter- 
nal coat, strengthened by fibrous tissue ; they always look toward the heart, 
and when closed prevent a return of blood in the veins. Valves are most 
numerous in the veins of the extremities, but are entirely absent in many 
others. 

The onward flow of blood in the veins is mainly due to the 
action of the heart ; but is assisted by muscular contraction of the veins 
themselves, and the respiratory movements. 

Muscular contraction, which is intermittent, aids the flow of blood in 
the veins by compressing them, and urging it onward. Regurgitation is 
prevented by the closure of the valves, which directs the current into anas- 
tomosing channels. 

Rhythmical movements of veins have been observed in some of the 
lower animals, aiding the onward current of blood. 

During inspiration, when the thorax is enlarged in all its diameters, 
the blood in the venae cavae flows into the heart with greater rapidity, and 
in larger quantity. The rapidity of the venous current is somewhat less 
than in the arteries, but becomes more rapid as it approaches the heart. 



RESPIRATION. 39 

Venous pressure. As the force of the heart is nearly expended in 
driving the blood through the capillaries, the pressure in the venous sys- 
tem is not very marked, not amounting in the jugular vein of a dog to 
more than ^th that of the carotid artery. 

The time required for a complete circulation of the blood throughout 
the vascular system has been estimated to be from 20 to 30 seconds, while 
for the entire mass of blood to pass through the heart 58 pulsations would 
be required, occupying 48 seconds. 

The forces keeping the blood in circulation are — 

1. Action of the heart. 

2. Elasticity of the arteries. 

3. Capillary force. 

4. Muscular contraction upon the veins. 

5. Respiratory movements. 

RESPIRATION. 

Respiration is the function by which oxygen is absorbed into the 
blood and carbonic acid exhaled. The appropriation of the oxygen and 
the evolution of carbonic acid takes place in the tissues as a part of the 
general nutritive process ; the blood and respiratory apparatus constituting 
the media by means'of which the interchange of gases is accomplished. 

The Respiratory Apparatus consists of the larynx, trachea and lungs. 

The Larynx is composed of firm cartilages, united together by liga- 
ments and muscles ; running antero-posteriorly across the upper opening 
are four ligamentous bands, the two superior or false vocal cords, and the 
two inferior or true vocal cords, covered by folds of mucous membrane. 
They are attached anteriorly to the thyroid cartilages and posteriorly to the 
arytenoid cartilages, and are capable of being separated so as to permit 
the passage of air by the contraction of the crico-thyroid muscles. 

The Trachea is a tube from four to five inches in length, three-quarters 
of an inch in diameter, extending from the cricoid cartilage of the larynx 
to the third dorsal vertebra, where it divides into the right and left bronchi. 
It is composed of a series of cartilaginous rings, which extend about two- 
thirds around its circumference, the posterior third being occupied by 
fibrous tissue and non-striated muscular fibres which are capable of dimin- 
ishing its calibre. 

The trachea is covered externally by a tough, fibro-elastic membrane, 
arid internally by mucous membrane, lined by columnar ciliated epithelial 
cells. The cilia are always waving from within outward. When the 



40 HUMAN PHYSIOLOGY. 

two bronchi enter the lungs they divide and- subdivide into numerous and 
smaller branches, penetrating the lung in every direction until they finally 
terminate in the pulmonary lobules. 

As the bronchial tubes become smaller their walls become thinner ; the 
cartilaginous rings disappear, but are replaced by irregular angular plates 
of cartilage ; when the tube becomes less than the ^-th of an inch in 
diameter they wholly disappear, and the fibrous and mucous coats blend 
together, forming a delicate, elastic membrane, with circular muscular 
fibres. 

The Lungs occupy the cavity of the thorax, are conical in shape, of a 
pink color, and a spongy texture. They are composed of an innumer- 
able number of pulmonary lobules, the T ^th of an inch in diameter, the 
ultimate terminations of the bronchial tubes ; the lobules are oblo'ng, vary 
in size, and consist of a collection of air cells or air vesicles ; the walls of 
the air cells are exceedingly delicate, and are lined internally by a layer 
of tessellated epithelium, externally by elastic fibres, which give to the 
lungs elasticity and distensibility. 

The Venous Blood is distributed to the lungs for aeration by the termi- 
nal branches of the pulmonary artery, which form a rich plexus of capillary 
vessels surrounding the air cells ; the air and blood are brought into inti- 
mate relationship, being separated only by the delicate'walls of the air cells 
and capillaries. 

The Pleura. Each lung is surrounded by a closed serous membrane, 
the pleura, one layer of which, the visceral, is reflected over the lung, the 
other, the parietal, reflected over the wall of the thorax ; between the two 
layers is a small amount of fluid which prevents friction during the play of 
the lungs in respiration. 

The lungs are nourished by blood from the bronchial arteries ramifying 
in the walls of the bronchial tubes and inter-lobular connective tissue. 

Respiratory movements. The movements of respiration are two, 
and consist of an alternate dilation and contraction of the chest, known as 
inspiration and expiration. 

1. Inspiration is an active process, the result of the expansion of the 
thorax, whereby air is introduced into the lungs. 

2. Expiration is a partially passive process, the result of contraction of 
the thorax, whereby the carbonic acid is expelled. 

In Inspiration the chest is enlarged by an increase in all its diameters, 
viz : — 

I. The vertical is increased by the contraction and descent of the 
diaphragm when it approximates a straight line. 



RESPIRATION. 41 

2. The antero-posterior and transverse diameters are increased by the 
elevation of the ribs and rotation upon their axes. 

In ordinary tranquil inspiration the muscles which elevate the ribs and 
thrust the sternum forward, are the external intercostals, running from 
above downward and forward, the sternal portion of the internal inter- 
cos tals and the lev at ores cost arum. 

In the extraordinary efforts of inspiration, when the capacity of the chest 
is increased to its utmost extent, auxiliary muscles are brought into play, 
viz : the sterno-mastoid, perforates, serratus magnus. 

In Expiration the diameters of the chest are all diminished, viz : 

1. The vertically the ascent of the diaphragm. 

2. The anteroposterior by a depression of the ribs and sternum. 

In ordinary expiration the muscles which contract the chest are the 
internal intercostals, the infra-costals and the triangularis stemi. 

Extraordinary expiration is produced by the auxiliary action of the 
abdominal and sacro-lumbalis muscles. 

Expiration is aided by the recoil of the elasticity of the lungs and ribs 
and the pressure of the air. 

Movements of the Glottis. At each inspiration the rima glottidis 
is dilated by a separation of the vocal cords, produced by the contraction 
of the crico-arytenoid muscles, so as to freely admit the passage of air into 
the lungs ; in expiration they fall passively together, but do not interfere 
with the exit of the air from the che^t. 

Nervous Mechanism of Respiration. The movements of respira- 
tion are involuntary and reflex, and are under the control of the medulla 
oblongata. 

This centre may be stimulated directly by the condition of the blood, or 
indirectly by reflex action ; an increase of carbonic acid or a diminution of 
oxygen in the blood causes an acceleration of the respiratory movements ; 
the reverse, a diminution. Again, the venous blood going to the lungs 
charged with carbonic acid stimulates the terminal filaments of the pneu- 
mogastric nerve, which stimulus is conveyed to the medulla, and excites 
the respiratory centre. In either case this centre reflects motor impulses 
to the respiratory muscles through the phrenic, intercostals, inferior laryn- 
geal and other nerves. 

Types of Respiration. The abdominal type is most marked in young 
children, irrespective of sex ; the respiratory movements being effected by 
the diaphragm and abdominal muscles. 

In the superior costal type, exhibited by the adult female, the respiratory 



42 HUMAN PHYSIOLOGY. 

movements are more marked in the upper part of the chest, from the 1st to 
the 7th ribs, permitting the uterus to ascend in the abdomen during preg- 
nancy without interfering with respiration. 

In the inferior costal type, manifested by the male, the movements are 
largely produced by the muscles of the lower portion of the chest, from the 
7th rib downward, assisted by the diaphragm. 

The respiratory movements vary according to age, sleep and exercise, 
being most frequent in early life, but averaging 20 per minute in adult 
life. They are diminished by sleep and increased by exercise. There are 
about four pulsations of the heart to each respiratory act. 

During inspiration, two sounds are produced; the one, heard in the 
thorax, in the trachea and larger bronchial tubes, is tubular in character; 
the other, heard in the substance of the lungs, is vesicular in character. 

AMOUNT OF AIR EXCHANGED IN RESPIRATION, AND CAPACITY 

OF LUNGS. 

The tidal or breathing volume of air, that which passes in and out of the 
lungs at each inspiration and expiration, is estimated at from 20 to 30 
cubic inches. 

The comple mental air is that amount which can be taken into the lungs 
by a forced inspiration, in addition to the ordinary tidal volume, and 
amounts to about 100 cubic inches. 

The reserve air is that which usually remains in the chest after the 
ordinary efforts of expiration, but which can be expelled by forcible expira- 
tion. The volume of.reserve air is also 100 cubic inches. 

Residual air. After the most forcible expiratory efforts there remains in 
the lungs a quantity of air which cannot be expelled, and which amounts 
to about 100 cubic inches, according to Dr. Hutchinson. 

The Vital Capacity of the chest indicates the amount of air that can 
be forcibly expelled from the lungs after the deepest possible inspiration, 
and is an index of an individual's power of breathing in disease and pro- 
longed severe exercise. The combined amounts of the tidal, the comple- 
mental and reserve air, 230 cubic inches, represents the vital capacity of an 
individual 5 feet, 7 inches in height. The vital capacity varies chiefly with 
stature. It is increased 8 cubic inches for every inch in height above this 
standard, and diminishes 8 cubic inches for each inch below it. 

The Tidal Volume of air is carried only into the trachea and larger 
bronchial tubes by the inspiratory movements. It reaches the deeper 
portions of the lungs in obedience to the law of diffusion of gases, which is 
inversely proportionate to the square root of their densities. 



RESPIRATION. 43 

The ciliary action of the columnar cells lining the bronchial tubes also 
assists in the interchange of the air and carbonic acid. 

The entire vohime of air passing in and out of the thorax in 24 hours is 
subject to great variation, but is estimated by Dr. Smith at 686,000 cubic 
inches, or 397 cubic feet. 

Composition of Air : Oxygen, 20.81 parts; nitrogen, 79.19, forming a 
mechanical mixture in which exist traces of carbonic acid and watery 
vapor. 

The changes in the air effected by respiration are — 
Loss of oxygen, to the extent of 4.782 per cent. 
Gain of carbonic acid, to the extent of 4.35 per cent. 
Increase of watery vapor and organic matter. 
Elevation of temperature. 
Increase and at times decrease of nitrogen. 
Gain of ammonia. 
The total quantity of oxygen withdrawn from the air and consumed by 
the body in 24 hours amounts to 18 cubic feet ; to obtain this quantity 400 
cubic feet of pure air are necessary. 

The quantity of carbonic acid exhaled in 24 hours varies greatly; Dr. 
Smith computed it at 24.208 cubic inches, containing 7.144 oz. of pure 
carbon. It is increased by muscular exercise ; nitrogenous food • tea 
coffee, and rice ; age, and by muscular development ; decreased by a low- 
ering of temperature ; repose ; gin and brandy, and a dry condition of the 
air. 

Condition of the Gases in the Blood. 

Oxygen is absorbed from the lungs into the arterial blood by the color- 
ing matter, hcemoglobin, with which it exists in a state of loose combina- 
tion, and is disengaged during the process of nutrition. 

Carbonic acid, arising in the tissues, is absorbed into the blood in conse- 
quence of its alkalinity ; where it exists in a state of simple solution and 
also in a state of feeble combination with soda and potassa, forming the 
bicarbonates ; it is liberated by pneumic acid in the pulmonary tissue. 

Nitrogen is simply in solution in the plasma. 

The amount of zvatery vapor thrown off from the lungs daily is about 
one pound, with which is mingled organic matter and ammonia. 

Changes in the Blood during Respiration. 

As the blood passes through the lungs it is changed in color, from the 
dark purple hue of venous blood to the bright scarlet of arterial blood. 

The heterogeneous composition of venous blood is exchanged for the 
uniform composition of the arterial. 



44 HUMAN PHYSIOLOGY. 

It gains oxygen and loses carbonic acid. 

Its coagulability is increased. Temperature is diminished. 

Asphyxia. If the supply of oxygen to the lungs be diminished and 
the carbonic acid retained in the blood, the normal respiratory movements 
cease, the condition of asphyxia ensues, which soon terminates in death. 

The phenomena of asphyxia are, violent spasmodic action of the respira- 
tory muscles, attended by convulsions of the muscles of the extremities, 
engorgement of the venous system, lividity of the skin, abolition of in- 
sensibility and reflex action, and death. 

The cause of death is a paralysis of the heart, from over distention by 
blood. The passage of the blood through the capillaries is prevented by 
contraction of the smaller arteries from irritation of the vaso-motor centre. 
The heart is enfeebled by a want of oxygen and inhibited in its action by 
the inhibitory centres. 

ANIMAL HEAT. 

The Functional Activity of all the organs and tissues of the body is 
attended by the evolution of heat, which is independent, for the most part, 
of external conditions. Heat is a necessary condition for the due perform- 
ance of all vital actions; though the body constantly loses heat by radia- 
tion and evaporation, it possesses the capability of renewing it and 
maintaining it at a fixed standard. The normal temperature of the body 
in the adult, as shown by means of a delicate thermometer placed in the 
axilla, ranges from 97. 25 Fahr. to 99. 5 Fahr., though the mean normal 
temperature is estimated by Wunderlich at 98. 6° Fahr. 

The temperature varies in different portions of the body, according to 
the degree to which oxidation takes place ; being the highest in the muscles 
during exercise, in the brain, blood, liver, etc. 

The conditions which produce variations in the normal tempera- 
ture of the body are : age, period of the day, exercise, food and drink, 
climate, season and disease. 

Age. At birth the temperature of the infant is about i° F. above that 
of the adult, but in a few hours falls to 95. 5 F., to be followed in the 
course of 24 hours by a rise to the normal or a degree beyond. During 
childhood the temperature approaches that of the adult ; in aged persons 
the temperature remains about the same, though they are not as capable 
of resisting the depressing effects of external cold as adults. A diurnal 
variation of the temperature occurs from i.8° F. to 3. 6° F. (Jiirgensen) ; 
the maximum occurring late in the afternoon, from 4 to 9 p.m., the mini- 
mum, early in the morning, from 1 to 7 A.M. 



ANIMAL HEAT. 45 

Exercise. The temperature is raised from i° to 2° F. during active con- 
tractions of the muscular masses, and is probably due to the increased 
activity of chemical changes ; a rise beyond this point being prevented by 
its diffusion to the surface, consequent on a more rapid circulation, radia- 
tion, more rapid breathing, etc. 

Food and drink. The ingestion of a hearty meal increases the tempera- 
ture but slightly ; an absence of food, as in starvation, produces a marked 
decrease. Alcoholic drinks, in large amounts, in persons unaccustomed 
to their use, cause a depression of the temperature amounting from i° to 2° 
F. Tea causes a slight elevation. 

External temperature. Long continued exposure to cold, especially if 
the body is at rest, diminishes the temperature from i° to 2° F., while ex- 
posure to a great heat slightly increases it. 

Disease frequently causes a marked variation in the normal temperature 
of the body, rising as high as 107 F. in typhoid fever, and 105 F. in pneu- 
monia ; in cholera it falls as low as 8o° F. Death usually occurs when 
the heat remains high and persistent, from 106 to no° F. ; the increase 
of heat in disease is due to excessive production rather than to dimin- 
ished elimination. 

The source of heat is to be sought for in the chemical combinations 
taking place during the general process of nutrition ; and the amount of 
its production is in proportion to the activity of the internal changes. 

Every contraction of a muscle, every act of secretion, each exhibition 
of nerve force, is accompanied by a change in the chemical composition of 
the tissues and an evolution of heat. The reduction of the disintegrated 
tissues to their simplest forms by oxidation ; the combination of the oxygen 
of the inspired air with the carbon and hydrogen of the blood and tissues, 
results in the formation of carbonic acid and water and the generation 
of a large amount of heat. 

Certain elements of the food, particularly the non-nitrogenized sub- 
stances, undergo oxidation without taking part in the formation of the 
tissues, being transformed into carbonic acid and water, and thus increase 
the sum of heat in the body. 

Heat-producing Tissues. All the tissues of the body add to the 
general amount of heat, according to the degree of their activity. But 
special structures, on account of their mass and the large amount of blood 
they receive, are particularly to be regarded as heat producers ; e. g. : — g 

I. During mental activity the brain receives nearly one-fifth of the 
entire volume of blood, and the venous blood returning from it is charged 
with waste matters, and its temperature is increased. 



46 HUMAN PHYSIOLOGY. 

2. The muscular tissue, on account of the many chemical changes 
occurring during active contractions, must be regarded as the chief heat- 
producing tissue. 

3. The secreting glands, during their functional activity, add largely to 
the amount of heat. 

Of the entire quantity of heat generated in the body, it is estimated 
that only a small proportion is utilized, as five-sixths escape by radiation 
and evaporation, the remaining one-sixth being utilized in keeping the 
body at the normal temperature standard, 98. 6° F., and in the production 
of muscular force. 

The body loses heat by radiation and evaporation from the general cuta- 
neous surface, the respiratory passages and by the urine and faeces. About 
75 per cent, of all the heat lost escapes from the skin. In passing through 
the lungs the temperature of the blood is lowered by about 2° Fahr. 

The nervous system influences the production of heat in a part, by 
increasing the amount of blood going through it by its action upon the 
vaso-motor nerves. Whether there exists a special heat centre has not 
been satisfactorily determined, though this is probable. 

SECRETION. 

The Process of Secretion consists in the separation of materials from 
the blood, which are either to be again utilized to fulfill some special pur- 
pose in the economy, or are to be removed from the body as excrementi- 
tious matter; in the former case they constitute the secretions, in the latter, 
the excretions. 

The materials which enter into the composition of the secretions are de- 
rived from the nutritive principles of the blood, and require special organs, 
e. g. gastric glands, mammary glands, etc., for their proper elaboration. 

The materials which compose the excretions pre-exist in the blood, and 
are the results of the activities of the nutritive process ; if retained within the 
body they exert a deleterious influence upon the composition of the blood. 

Destruction of a secreting gland abolishes the secretion peculiar to it, 
and it cannot be formed by any other gland ; but among the excreting organs 
there exists a complementary relation, so that if the function of one organ be 
interfered with, another performs it, to a certain extent. 

CLASSIFICATION OF THE SECRETIONS. 
PERMANENT FLUIDS. 

Serous fluids. Vitreous humor of the eye. 

Synovial fluid. Fluid of the labyrinth of the internal 

Aqueous humor of the eye. ear. 

Cerebro-spinal fluid. 



SECRETION. 4/ 

TRANSITORY FLUIDS. 

Mucus. Gastric juice. 

Sebaceous matter. Pancreatic juice. 

Cerumen (external meatus). Secretion from Brunner's glands. 

Meibomian fluid. Secretion from Lieberkiihn's glands. 

Milk and colostrum. Secretion from follicles of the large 

Tears. intestine. 

Saliva. Bile (also an excretion.) 

EXCRETIONS. 

Perspiration and the secretion of Urine. 

the axillary glands. . Bile (also a secretion). 

FLUIDS CONTAINING FORMED ANATOMICAL ELEMENTS.. 

Seminal fluid, containing spermatozoids. Fluid of the Graafian follicles. 

The essential apparatus for secretion is a delicate homogeneous, 
structureless membrane, on one side of which, in close contact, is a. capillary 
plexus of blood vessels, and on the other side a layer of cells whose physio- 
logical function varies in different situations. 

Secreting organs may be divided into membranes and glands. 

Serous membranes usually exist as closed sacs, the inner surface of 
which is covered by pale, nucleated epithelium, containing a small amount 
of secretion. 

The serous membranes are the pleura, peritoneum, pericardium, synovial 
sacs, etc. 

The serous fluids are of a pale amber color, somewhat viscid, alkaline, 
coagulable by heat, and resemble the serum of the blood ; their amount is 
but small ; the pleural from 4 to 7 drachms ; the peritoneal from 1 to 4 
ounces ; the pericardial from 1 to 3 drachms. 

The synovial fluid 'is colorless, alkaline, and extremely viscid, from the 
presence of synovine. 

The function of serous fluids is to moisten the opposing surfaces, so as 
to prevent friction during the play of the viscera. 

The mucous membranes are soft and velvety in character, and line the 
cavities and passages leading to the exterior of the body, e. g., the gastro- 
intestinal, pulmonary and genito-urinary \ They consist of a primary 
basement membrane covered with epithelial cells, which, in some situations, 
are tessellated, in others, columnar. 

Mucus is a pale, semi-transparent, alkaline fluid, containing epithelial 
cells and leucocytes. It is composed, chemically, of water, an albumin- 



48 HUMAN PHYSIOLOGY. 

ous principle, mucosine, and mineral salts; the principal varieties are nasal, 
bronchial, vaginal and urinary. 

Secreting Glands are formed of the same elements as the secreting 
membranes ; but instead of presenting flat surfaces, are involuted, forming 
tubules, which may be simple follicles, e. g., mucous, uterine or intestinal ; 
or compound follicles, e. g., gastric glands, mammary glands; or racemose 
glands, e. g., salivary glands and pancreas. They are composed of a 
basement membrane, enveloped by a plexus of blood vessels, and are lined 
by epithelial and true secreting cells, which in different glands possess the 
capability of elaborating elements characteristic of their secretions. 

In the production of the secretions two essentially different processes 
are concerned, viz. : — 

1. Chemical. The formation and elaboration of the characteristic organic 
ingredients of the secreting fluids, e. g., pepsin, pancreatin, takes place 
during the intervals of glandular activity, as a part of the general function 
of nutrition. They are formed by the cells lining the glands, and can 
often be seen in their interior with the aid of the microscope, e. g., bile in 
the liver cells, fat in the cells of the mammary gland. 

2. Physical. Consisting of a transudation of water and mineral salts from 
the blood into the interior of the gland. 

During the intervals of glandular activity, only an amount of blood passes 
through the gland sufficient for proper nutrition ; when the gland begins to 
secrete, under the influence of an appropriate stimulus, the blood vessels 
dilate and the quantity of blood becomes greatly increased beyond that 
flowing through the gland during its repose. 

Under these conditions a transudation of water and salts takes 
place, washing out the characteristic ingredients, which are discharged by 
the gland ducts. The discharge of the secretions is intermittent ; they are 
retained in the glands until they receive the appropriate stimulus, when 
they pass into the larger ducts by the vis-a-tergo, and are then discharged 
by the contraction of the muscular walls of the ducts. 

The activity of glandular secretion is hastened by an increase in the 
blood pressure and retarded by a diminution. 

The nervous ceittres in the medulla oblongata influence secretion, (i) by 
increasing or diminishing the amount of blood entering a gland; (2) by 
exerting a direct influence upon the secreting cells themselves, the centres 
being excited by reflex irritation, mental emotion, etc. 



MILK. 49 

MAMMARY GLANDS. 

The Mammary Glands secrete the milk, and undergo at different 
periods of life remarkable changes in size and structure. Though rudi- 
mentary in childhood, they gradually increase in size as the young female 
approaches puberty. 

The gland presents, at its convexity, a small prominence of skin, the 
nipple, surrounded by an areola of a deeper tint. It is covered anteriorly 
by a layer of adipose tissue and posteriorly by a fibrous structure which 
attaches it loosely to the pectoralis muscle. 

During utero-gestation the mammas become large, firm, well developed 
and lobulated; the areola becomes darker and the veins more prominent. 
In the intervals of lactation the glands gradually shrink in size to their 
original condition, undergo involution, and become non-secreting organs. 

Structure of the Mammae. The mamma is a conglomerate gland, 
consisting of a number of lobes, from 15 to 20 in number, each of which is 
subdivided into lobules made up of glaitd vesicles or acini. The ducts 
which convey the secretion to the exterior, the lactiferous ducts, open by 
15 to 20 orifices upon the surface of the nipple, at the base of which they 
are dilated to form little reservoirs in which the milk collects during the 
periods of active secretion. 

The walls of the lacteal ducts consist of white, fibrous tissue, and non- 
striated muscular fibres, lined by short columnar cells, which disappear 
during active lactation. The ducts measure about the y^th of an inch in 
diameter ; as they pass into the substance of the gland, each duct divides 
into a number of branches, which are distributed to distinct lobules, and 
terminate in the acini. 

An acinus is made up of a number of vesicles composed of a homoge- 
neous membrane, lined by pavement epithelium. The gland vesicles are 
held together by white, fibrous tissue, which unites the lobules into lobes. 

MILK. 

Milk has a pale, blue color, is almost inodorous, of a sweetish taste, an 
alkaline reaction, and a specific gravity varying from 1.025 to 1-046. 
Examined microscopically it is seen to contain an immense number of 
globules, measuring the T o^o tn °f an i ncn m diameter, suspended in a 
clear fluid; these are the milk globules, formed of a small mass of oily 
matter covered by a layer of albumen. 

The quantity of milk secreted by the human female in 24 hours, during 
the period of lactation, is about two to three pints ; the quantity removed 
by the infant from a full breast at one time being about two ounces. 



50 HUMAN PHYSIOLOGY. 

COMPOSITION OF MILK. 

Water 800.00 

Proteids, including casein and serum albumen 35 .00 

Fatty matter (butter) 25.00 

Sugar (lactose) with extractives 48.00 

Salts 2 .00 

1000.00 

Casein is the nutritive principle of milk, and constitutes its most import- 
ant ingredient. It is held in solution by an alkali, but upon the addition 
of an acid it undergoes coagulation, passing into a semi-solid form. The 
presence of lactic acid, resulting from a transformation of milk sugar, 
causes spontaneous coagulation to take place. 

The fatty matter is more or less solid at ordinary temperature, and con- 
sists of margarine and oleine ; when subjected to the churning process the 
globules run together and fGrm a coherent mass, the butter. 

When milk is allowed to stand for a varying length of time the fat glob 
ules rise to the surface, forming a layer more or less thick, the cream. 

Milk sugar or lactose is an important ingredient in the food of the young 
child ; it is readily transformed into lactic acid in the presence of nitro- 
genized ferments. 

Influences modifying the secretion. During lactation there is a 
demand for an increased amount of fluid, and if not supplied, the amount 
of milk secreted is diminished. Good food in sufficient quantity is neces- 
sary for the proper elaboration of milk, though no particular article influ- 
ences its production. 

Mental emotion at times influences the character of the milk, decreasing 
the amount of its different constituents. 

Mechanism of Secretion. The water and salts pre-exist in the blood 
and pass into the gland vesicles by osmosis. The casein, fatty matter and 
sugar appear only in the mammary gland, but the mechanism of their for- 
mation is not understood. 

Colostrum is a yellowish, opaque fluid, formed in the mammary gland 
towards the latter period of utero-gestation ; it consists of water, albumen, 
fat, sugar and salts, and acts as a laxative to the newly born infant. 

VASCULAR OR DUCTLESS GLANDS. 

The Vascular Glands are regarded as possessing the power of acting 
upon certain elements of the food and aiding the process of sanguinifi- 
cation ; of modifying the composition of the blood as it flows through 
their substance, by some act of secretion. 



VASCULAR GLANDS. 51 

The vascular glands are the spleen, suprarenal capsules, thyroid and 
thymus glands. 

The Spleen is about 5 inches in length, 6 ounces in weight, of a 
dark bluish color, and situated in the left hypochondriac region. It is 
covered externally by a reflection of the peritoneum, beneath which is the 
proper fibrous coat, composed of areolar and elastic tissue and non-striated 
muscular fibres. From the inner surface of the fibrous envelope, processes 
or trabecule are given off, which penetrate the substance of the gland, 
forming a network, in the meshes of which is contained the spleen pulp. 
The splenic artery divides into a number of branches, some of which, 
when they become very minute, pass directly into veins, while others ter- 
minate in true capillaries. 

As the capillary vessels ramify through the substance of the gland their 
walls frequently disappear and the blood passes from the arteries into the 
veins through lactince (Gray). 

The sple?tic or Malpighian coipuscles are small bodies, spherical or ovoid 
in shape, the ^th of an inch in diameter, situated upon the sheaths of the 
small arteries. They consist of a delicate membrane, containing a semi- 
fluid substance composed of numerous small cells resembling lymph cor- 
puscles. The spleen pulp is a dark red, semi-fluid substance, of a soft con- 
sistence, contained in the meshes of the trabeculae. In it are found 
numerous corpuscles, like those observed in the Malpighian bodies, blood 
corpuscles in a natural and altered condition, nuclti and pigment granules. 

Function of the Spleen. Probably influences the preparation of the 
albuminous food for nutrition ; during digestion the spleen becomes larger, 
its contents are increased in amount, and after digestion it gradually dimin- 
ishes in size, returning to the normal condition. 

The red corpuscles are here disintegrated, after having fulfilled their function 
in the blood; the splenic venous blood containing relatively a small quantity. 

The white corpuscles appear to be increased in number, the blood of the 
splenic vein containing an unusually large proportion. 

The spleen serves also as a reservoir for blood when the portal circula- 
tion becomes obstructed. 

The nervous system controls the enlargement of the spleen ; division of 
the nerves produces dilatation of the vessels, stimulation contracts them. 

The Supra -Renal Capsules are triangular, flattened bodies, situated 
above the kidney. They are invested by a fibrous capsule sending in tra- 
beculae, forming the framework. The glandular tissue is composed of two 
portions, a cortical and medullary. The cortical being made up of small 
cylinders lined by cells and containing an opaque mass, nuclei and granu- 



52 HUMAN PHYSIOLOGY. 

lar matter. The medullary consists of a fibrous network containing in the 
alveoli nucleated protoplasm. 

The Thyroid gland consists of a fibrous stroma, containing ovoid 
closed sacs, measuring on the average ^th of an inch, formed of a delicate 
membrane lined by cells ; the contents of the sacs consist of yellowish 
albuminous fluid. 

The Thymus gland is most developed in early life and almost disap- 
pears in the adult. It is divided by processes of fibrous tissue into lobules, 
and these again into follicles which contain lymphoid corpuscles. 

The functions of the vascular glands appear to be the more complete 
elaboration of the blood, necessary for proper nutrition ; they are most 
highly developed during infancy and embryonic life, when growth and de- 
velopment are most active. ' 

EXCRETION. 

The Principal Excrementitious Fluids discharged from the body are 
the urine, perspiration, and bile; they hold in solution principles of waste 
which are generated during the activity of the nutritive process, and are the 
ultimate forms to which the organic constituents are reduced in the body. 
They also contain inorganic salts. 

The Urinary Apparatus consists of the kidneys, ureters and bladder. 
KIDNEYS. 

The Kidneys are the organs for the excretion of urine ; they resemble 
a bean in shape, are from four to five inches in length, two in breadth, and 
weigh from four to six ounces. 

They are situated in the lumbar region, one on each side of the verte- 
bral column, behind the peritoneum, and extend from the nth rib to the 
crest of the ilium ; the anterior surface is convex, the posterior concave, and 
presents a deep notch, the hilum. 

The kidney is surrounded by a thick layer of fat, beneath which is the 
fibrous coat, thin and smooth, composed of dense white fibrous tissue in- 
termingled with elastic fibres. It is adherent to the surface of the organ, 
but can easily be removed by dissection. 

The substance of the kidney is dense, but friable ; upon making 
a longitudinal section, and dividing it, there is presented a cavity, the 
pelvis, lined by the proper fibrous coat and occupied by the expanded por- 
tion of the ureter. 

The kidney exhibits two structures, viz : — 

I. An external ox cortical portion, about ^th of an inch in diameter, of a 
reddish color, and somewhat granular. 



EXCRETION. 53 

2. An internal or medullary portion, of a dark red color, arranged in 
the form of pyramids, the bases of which are directed towards the cortical 
portion, and the apices toward the pelvis, into which they project, and 
are covered by the calyces. 

The Cortical portion of the kidney consists of a delicate matrix con- 
taining an immense number of tubules, having a markedly convoluted 
appearance, and interlacing in every direction (the tubules of Ferrein). 
Throughout its structure are numerous ovoid bodies, the Malpighian bodies, 
which are the flask-like terminations of the convoluted tubules : these tubes 
are composed of a delicate homogeneous membrane lined by nucleated 
cells. ; After pursuing a most intricate course in the cortical portion, they 
become narrower and form loops which dip into the pyramidal portion 
(Henle's tubules) returning upon themselves, to finally terminate in the 
straight tubes of the pyramids. 

The Malpighian bodies, the dilated extremities of the convoluted 
tubes, consist of a little sac, which is ovoid in shape, measuring about the 
2-jjoth of an inch in diameter, and contains a tufted mass of minute blood 
vessels, over the surface of which is reflected a layer of cells. 

Medullary Substance. The conical masses, the pyramids of Malpi- 
ghi, consist of a number of straight tubes, which commence at the apex by 
from 10 to 20 openings ; and as they pass towards the cortical portion, they 
divide and subdivide at acute angles, until a large mass of tubes is pro- 
duced. These tubes are on the average about -^Jo tn °f an mc ^ m diame- 
ter, and composed of a thin, but firm, elastic, structureless membrane, lined 
by polygonal nucleated cells, which reduce the diameter of the lumen of 
the tube about two-thirds ; these are the straight tubes of Bellini. 

Blood vessels of the Kidney. The renal artery is of large size and 
enters the organ at the hiium ; it divides into several large branches, 
which penetrate the substance of the kidney, between the pyramids, at 
the base of which they form an anastomosing plexus, which completely 
surrounds them. From this plexus vessels follow the straight tubes towards 
the apex, while others entering the cortical portion, divide into small twigs 
which enter the Malpighian body and form a mass of convoluted vessels, 
the glomerulus. After circulating through the Malpighian tuft the blood 
is gathered together by two or three small veins, which again subdivide 
and form a fine capillary plexus, which envelops the convoluted tubules ; 
from this plexus the veins converge to form the emulgent vein, which 
empties into the vena cava. 

The Nerves of the kidney follow the course of the blood vessels and 
are derived from the renal plexus. 



54 HUMAN PHYSIOLOGY. 

The Ureter is a membranous tube, situated behind the peritoneum, 
about the diameter of a goose quill,- 18 inches in length, and extends from 
the pelvis of the kidney to the base of the bladder, which it perforates in " 
an oblique direction. It is composed of 3 coats, fibrous, muscular and 
mucous. 

The Bladder is a temporary reservoir for the reception of the urine 
prior to its expulsion from the body ; when fully distended it is ovoid in 
shape, and holds about one pint. It is composed of four coats, serous y 
mtiscular, the fibres of which are arranged longitudinally and circularly, 
areolar and mucous. The orifice of the bladder is controlled by the 
sphincter vesicce, a muscular band, about half an inch in width. 

As soon as the urine is formed it passes through the tubuli urini- 
feri into the pelvis, and from thence through the ureters into the bladder, 
which it enters at an irregular rate. Shortly after a meal, after the ingestion 
of large quantities of fluid, and after exercise the urine flows into the bladder 
quite rapidly, while it is reduced to a few drops during the intervals of 
digestion. It is prevented from regurgitating into the ureters by lying ob- 
liquely between the mucous and muscular coats. 

Micturition is accomplished by the involuntary contraction of the mus- 
cular coat excited by reflex action, assisted by the abdominal muscles and 
diaphragm. Towards the end of the act the accelerator urince hastens the 
stream and expels the last few drops. 

The nerve centre controlling this movement, the genito spinal, resides in 
the spinal cord opposite the 4th lumbar vertebra. 

URINE. 

Normal Urine is of a pale yellow or amber color, perfectly transpa- 
rent, with an aromatic odor, an acid reaction, a specific gravity of 1.020, 
and a temperature when first discharged of ioo° Fahr. * 

The color varies considerably in health, from a pale yellow to a brown 
hue, due to the presence of the- coloring matter, urobilin or urochroine. 

The transparency is diminished by the presence of mucus, the calcium 
and magnesium phosphates and the mixed urates. 

The reaction is slightly acid, caused by the acid phosphate of sodium. 
After standing for a short time, an increased acidity is observed, due to an 
acid fermentation, from the presence of mucus. The urea is converted 
into ammonium carbonate, giving rise to a strong ammoniacal odor. 

The specific gravity varies from 1. 010 to 1.025. 

The qua?ttity of urine excreted in 24 hours is between 40 and 50 fluid 
ounces, but ranges above and below this standard. 



55 



The odor is characteristic, and caused by the presence of taurylic and 
phenylic acids, but is influenced by vegetable foods and other substances 
eliminated by the kidneys. 

COMPOSITION OF URINE. 
Water 967. 



Urea. 



Other nitrogenized crystalline bodies, uric acid, prin- 
cipally in the form of alkaline urates. 

Creatin, creatinin, xanthin, hypoxanthin. 

Hippuric acid, leucin, tyrosin, taurin, cystin, all in 
small amounts, and not constant. 

Mucous and pigment. 
Salts : 

Inorganic, principally sodium and potassium sul- 
phates, phosphates and chlorides, with magnesium and 
calcium phosphates, traces of silicates and chlorides. 

Organic; lactates, hippurates acetates, formates, 
which appear only occasionally. 

Sugar 

Gases (nitrogen and carbonic acid principally). 



14.230 



10.635 



•135 



a trace. 



1000.00 
The Average Quantity of the principal constituents excreted in 24 
hours is as follows, viz : — 

Water... , 52 fluid oz. 

Urea S I2 -4- g rams - 

Uric acid 8.5 

Phosphoric acid 45.0 

Sulphuric acid „ ' 3 1 . 1 1 

Inorganic salts * 323.25 

Lime and magnesia 6.5 

To Determine the amount of solid matters in any given amount of 
urine, multiply the last two figures of the specific gravity by the coefficient 
of Haeser, 2.33 ; ^.^.,'in 1000 grains of urine having a specific gravity 1.022, 
there are contained 22x2.33 = 51.26 grains of solid matter. 

The Elimination of the urinary constituents is accomplished by the 
two processes of filtration and secretion. 

I. By Filtration the water and mineral salts are removed from the 
blood, and takes place, for the most part, in the Malpighian corpuscles, by 



56 HUMAN PHYSIOLOGY. 

the process of osmosis. The amount of these constituents eliminated 
varies with the pressure of blood in the renal arteries. All of the agen- 
cies which increase the general blood pressure increase the quantity of 
urine. 

Season. In summer, while the capillary vessels of the skin are dilated, 
and perspiration is abundant, there is a diminished blood pressure, and a 
consequent diminution in the amount of urine ; in winter the reverse takes 
place. 

During sleep the renal excretion is diminished, but increased in the 
morning hours, and especially after the ingestion of hearty meals. 

The nervous syste?n influences the secretion of urine. Irritation of the 
medulla oblongata, a little above the origin of the pneumogastric and 
auditory nerves, increases the quantity; division of the renal nerves 
destroys the nutrition of the kidney, and thus interferes with the elimina- 
tion of the urine. Mental emotion, fear, anxiety etc., increase the amount 
secreted. 

2. Secretion. While it is established that the Malpighian corpuscles 
permit the filtration of water and salts, it is also shown that the renal epi- 
thelial cells lining the convoluted tubes are the agencies by which the solid 
matters, as urea, creatin, etc., are removed from the blood by a process of 
true secretion, which is independent of blood pressure and caused by the 
presence of these ingredients in the blood. 

Urea is the most important of the organic constituents of the urine. It 
is a colorless, neutral substance, crystallizing in four-sided prisms, soluble 
in boiling alcohol and water; when subjected to prolonged boiling it is 
decomposed, with the production of ammonium carbonate. 

Urea is not formed in the kidneys, but pre-exists in the blood. 

The Amount of Urea excreted in 24 hours is estimated at about 500 
grains ; it is increased during the waking hours, by an animal diet, and by 
prolonged muscular exertion ; diminished during sleep and by non-nit.ro- 
genized food. 

Source. Urea results from an imperfect oxidation of the albuminous 
principles of the food, and from a disintegration of the organic constituents 
of the tissues. 

Uric acid, or lithic acid, is a constant ingredient of the urine ; the amount 
excreted daily is about 8 grains ; it is increased by nitrogenized, decreased 
by non -nitrogenized food. It exists in the urine in a free state, and as the 
urate of soda. It arises from the disassimilation of albuminous compounds, 
and when secreted in excess is deposited in a crystalline form, as a brown 
or " brick-red" sediment, with the sodium and ammonium urates. 



LIVER. 57 

Creatin is a colorless, transparent substance, crystallizing in prisms, 
found in blood, kidneys, and muscular tissue ; by boiling in acid solutions 
it is transformed into 

Creatinin, which resembles creatin chemically. It is soluble in water 
and alcohol, and crystallizes in colorless prisms; about 15 grains are 
excreted daily. 

The earthy phosphates are insoluble in water but held in solution in the 
urine by the acid reaction. If the urine becomes alkaline, they are de- 
posited copiously, and yet may not be increased in quantity; from 15 to 25 
grains are excreted in 24 hours. The sulphates are those of sodium and 
potassium ; they are very soluble, and do not appear as a precipitate ; the 
average quantity excreted in 24 hours is about 60 grains. 

Abnormal ingredients appear in the urine at times, in pathological con- 
ditions, e. g., sugar, albumen, biliary salts, etc. 

The gases of the urine are carbonic acid and nitrogen. 

LIVER. 

The Liver is a highly vascular, conglomerate gland, appended to the 
alimentary canal, and performs the triple office of (1) excreting bile, (2) 
elaborating blood, and (3) secreting glycogen. 

It is the largest gland in the body, weighing about 4^ pounds ; it is 
situated in the right hypochondriac region, and retained in position by five 
ligaments, four of which are formed by duplicatures of the peritoneal in- 
vestment. 

The proper coat of the liver is a thin but firm fibrous membrane, closely 
adherent to the surface of the organ, which it penetrates at the transverse 
fissure, and follows the vessels in their ramifications through its substance, 
constituting G lis sort s capsule. 

Structure of the Liver. The liver is made up of a large number of 
small bodies, the lobules, rounded or ovoid in shape, measuring the ^th 
of an inch in diameter, separated by a space in which are situated blood 
vessels, nerves, hepatic ducts and lymphatics. 

The lobules are composed of cells, which, when examined microscopi- 
cally, exhibit a rounded or polygonal shape, and measure, on the average, 
the T o^oo tn °f an ^ ncn m diameter; they possess one, and at times two, 
nuclei ; they also contain globules of fat, pigment matter, and animal 
starch. The cells constitute the secreting structure of the liver, and are 
the t)'ue hepatic cells. 

The Blood vessels which enter the liver are (1) The portal vein, 
made up of the gastric, splenic, superior and inferior mesenteric veins ; (2) 
E 



58 HUMAN PHYSIOLOGY. 

the hepatic artery, a branch of the cceliac axis ; both of which are invested by 
a sheath of areolar tissue ; the vessels which leave the liver are the hepatic 
veins } originating in its interior, collecting the blood distributed by the 
portal vein and hepatic artery, and conducting it to the ascending vena cava. 

Distribution of Vessels. The portal vein and hepatic artery, upon 
entering the liver, penetrate its substance, divide into smaller and smaller 
branches, occupy the spaces between the lobules, completely surrounding 
and limiting them, and constitute the inter-lobular vessels. The hepatic 
artery, in its course, gives off branches to the walls of the portal vein, 
and Glisson's capsule, and finally empties into the small branches of the 
portal vein in the interlobular spaces. 

The interlobular vessels form a rich plexus around the lobules, from 
which branches pass to neighboring lobules and enter their substance, 
where they form a very fine network of capillary vessels, ramifying over the 
hepatic cells, and among which the various functions of the liver are per- 
formed. The blood is then collected by small veins, converging towards 
the centre of the lobule, to form the intra-lobular vein, which runs through 
its long axis and empties into the sub-lobular vein. The hepatic veins are 
formed by the union of the sub-lobular veins, and carry the blood to the 
ascending vena cava ; their walls are thin and adherent to the substance of 
the hepatic tissue. 

The Hepatic ducts or Bile capillaries originate within the lobules, 
in a very fine plexus lying between the hepatic cells; whether the smallest 
vessels have distinct membranous walls, or whether they originate in the 
spaces between the cells by open orifices, has not been satisfactorily de- 
termined. 

The bile channels empty into the interlobular ducts, which measure 
about the 2 Fo"o^ n °^ an incn in diameter, and are composed of a thin, homo- 
geneous membrane lined by flattened epithelial cells. 

As the interlobular bile ducts unite to form larger trunks, they receive 
an external coat of fibrous tissue, which strengthens their walls ; they 
finally unite to form one large duct, the hepatic duct, which joins the cystic 
duct ; the union of the two, forms the ductus communis choledochus, which 
is about three inches in length, the size of a goose quill, and opens into 
the duodenum. 

The Gall Bladder is a pear-shaped sack, about four inches in length, 
situated in a fossa on the under surface of the liver. It is a reservoir for 
the bile, and is capable of holding about one ounce and a half of fluid. It 
is composed of three coats, (1) serous, a reflection of the peritoneum, (2) 
fibrous and muscular, (3) mucous. 



LIVER. 59 

(i) Bile. Mechanism of its Secretion. Bile does not preexist in 
the blood, but is formed in the interior of the hepatic cells, from materials 
derived from the venous as well as arterial blood. The secreted bile is 
then taken up by the delicate plexus of vessels, from which it passes into 
the larger ducts, and finally empties either into the intestine or is regur- 
gitated backward into the gall bladder, in which it is stored up during the 
intervals of digestion. 

Although the secretion of bile is constantly taking place, it is only when 
the food passes into the intestinal canal that this fluid is discharged abund- 
antly, under the influence of the contraction of the walls of the gall blad- 
der ; it increases in amount during the period of active digestion, from the 
2d to the 8th hour, and then gradually diminishes. 

The Bile is both a secretion and an excretion; it contains new constitu- 
ents which are formed only in the substance of the liver, and are destined 
to play an important part ultimately in nutrition ; it contains also waste 
ingredients which are discharged into the intestinal canal and eliminated 
from the body. 

The physical properties and. functions of bile have been considered 
under the head of digestion (see page 24). 

(2) Elaboration of Blood. Besides the capability of secreting bile, the 
liver possesses the property of so acting upon and modifying the chemical 
composition of the products of digestion, .as they traverse its substance, that 
they readily assimilate with the blood, and are transformed into materials 
capable of being converted into the elements of the blood and solid tissues. 

The albuminose particularly requires the modifying influence of the 
liver ; for if it be removed from the portal vein and introduced into the 
jugular vein, it is at once removed from the blood by the action of the 
kidneys. 

The blood of the hepatic vein differs from the blood of the portal vein, 
in being richer in blood corpuscles, both red and white ; its plasma is 
more dense, containing a less percentage of water and a greater amount 
of solid constituents, but no fibrin; its serum contains less albumen, fat 
and salts, but its sugar is increased. 

(3) Glycogenic Function. In addition to the two preceding func- 
tions, Bernard, in 1848, demonstrated the fact that the liver, during life, 
normally produces a sugar-forming substance, analogous in its chemical 
composition to starch, which he termed glycogen; also that when the 
liver is removed from the body, and its blood vessels thoroughly washed 
out, after a few hours, sugar again makes its appearance, in abundance. 



60 HUMAN PHYSIOLOGY. 

It can be shown to exist in the blood of the hepatic vein as well as m 
a decoction of the liver substance, by means of either Trommer's or 
Fehling's tests, even when the blood of the portal vein does not contain a 
trace of sugar. 

Glycogen appears to be formed de novo in the liver cells, from materials 
derived from the food, whether the diet be animal or vegetable ; though a 
larger percentage of sugar appears in the hepatic vein when the animal is 
fed on starchy and saccharine, than when fed on animal food. 

Destination of Glycogen. During life, as fast as the glycogenic 
matter is formed, it is converted into sugar, by means of a ferment, and 
carried from the liver by the blood into the lungs, where it undergoes com- 
bustion. 

Glycogen, when obtained from the liver, is an amorphous, starch-like 
substance, of a white color, tasteless and odorless, and soluble in water ; 
by boiling with dilute acids, or subjected to the action of an animal fer- 
ment, it is easily converted into glucose. When an excess of sugar is gene- 
rated by the liver, it can be found, not only in the blood of the hepatic 
vein, but also in other portions of the body ; under these circumstances it 
is eliminated by the kidneys, appearing in the urine, constituting the con- 
dition of glycosuria. 

The nervous system influences the production of the glycogenic 
matter; irritation of the medulla oblongata, between the auditory and pneu- 
mogastric nerves, is followed by an increase in the production of sugar, 
and its appearance in the urine, which, however, is only temporary. 

SKIN. 

The Skin, the external investment of the body, is a most complex and 
important structure, serving (i) as a protective covering; (2) an organ for 
tactile sensibility ; (3) an organ for the elimination of excrementitious 
matters. 

The Amount of Skin investing the body of a man of average size 
is about 20 feet, and varies in thickness, in different situations, from the 
i^th to the T ijoth of an inch. 

The skin consists of two principal layers, viz, a deeper portion, the 
Corium, and a superficial portion, the Epidermis.* 

The Corium, or Cutis Vera, may be subdivided into a reticulated and 
a papillary layer. The for?ner is composed of white fibrous tissue, non- 
striated muscular fibres and elastic tissue, interwoven in every direction, 
forming an areolar network, in the meshes of which are deposited masses 
of fat, and a structureless amorphous matter ; the latter is formed mainly of 



SKIN. 61 

club-shaped elevations or projections of the amorphous matter, constituting 
the papilla ; they are most abundant, and well developed, upon the palms 
of the hands and the soles of the feet ; they average the T ^th of an inch 
in length, and may be simple or compound ; they are well supplied with 
nerves, blood vessels and lymphatics. 

The Epidermis or scarf skin is an extra vascular structure, a pro- 
duct of the true skin, and composed of several layers of cells. It may be 
divided into two layers, the rete mucosum or the Malpighian layer, and the 
horny or corneous. 

The former closely applies itself to the papillary layer of the true skin, 
and is composed of large, nucleated cells, the lowest layer of which, the 
"prickle cells," contain pigment granules, which give to the skin its vary- 
ing tints in different individuals and in different races of men ; the more 
superficial cells are large, colorless, and semi-transparent. The latter, 
the corneous layer, is composed of flattened cells, which, from their expo- 
sure to the atmosphere," are hard and horny in texture ; it varies in thick- 
ness from y% of an inch on the palms of the hands and feet, to the -g^oth 
of an inch in the external auditory canal. 

APPENDAGES OF THE SKIN. 

Hairs are found in almost all portions of the body, and can be divided 
into (i) long, soft hairs, on the head; (2) short, stiff hairs, along the edges 
of the eyelids and nostrils; (3) soft, downy hairs, on the general cutane- 
ous surface. They consist of a root and a shaft, which is oval in shape, 
and about the ¥ -jjo tn °f an mcn m diameter ; it consists of fibrous tissue, 
covered externally by a layer of imbricated cells, and internally by cells 
containing granular and pigment material. 

The root of the hair is embedded in the hair follicle, formed by a tubular 
depression of the skin, extending nearly through to the subcutaneous tissue ; 
its walls are formed by the layers of the corium, covered by epidermic 
cells. At the bottom of the follicle is a papillary projection of amorphous 
matter, corresponding to a papilla of the true skin, containing blood vessels 
and nerves, upon which the hair root rests. The investments of the 'hair 
roots are formed of epithelial cells, constituting the internal and external 
root sheaths. 

The hair protects the head from the heat of the sun and cold, retains 
the heat of the body, prevents the entrance of foreign matter into the lungs, 
nose, ears, etc. The color is due to the pigment matter, which, in old age, 
becomes more or less whitened. 

The Sebaceous Glands, imbedded in the true skin, are simple and 
compound racemose glands, opening, by a common excretory duct, upon 



62 HUMAN PHYSIOLOGY. 

the surface of the epidermis or into the hair follicle. They aYe found in 
all portions of the body, most abundantly in the face, and are formed by a 
delicate, structureless membrane, lined by flattened polyhedral cells. The 
sebaceous glands secrete a peculiar oily matter, the sebum, by which the 
skin is lubricated and the hairs softened ; it is quite abundant in the region 
of the nose and forehead, which often present a greasy, glistening appear- 
ance ; it consists of water, mineral salts, fatty globules, and epithelial cells. 
The vernix caseosa which frequently covers the surface of the foetus at 
birth consists of the residue of the sebaceous matters, containing epithelial 
cells and fatty matters ; it seems to keep the skin soft and supple, and 
guards it from the effects of the long continued action of water. 

The Sudoriparous Glands excrete the sweat ; they consist of a mass 
or coil of a tubular gland duct, situated in the derma and in the sub- cuta- 
neous tissue ; average the y^th of an inch in diameter, and are surrounded 
by a rich plexus of capillary blood vessels. From this coil the duct passes 
in a straight direction up through the skin to the epidermis, where it makes 
a few spiral turns and opens obliquely upon the surface. The sweat 
glands consist of a delicate homogeneous membrane lined by epithelial 
cells, whose function is to extract from the blood the elements existing in 
the perspiration. 

The glands are very abundant all over the cutaneous surface, as many 
as 3528 to the square inch, according to Erasmus Wilson. 

The Perspiration is an excrementitous fluid, clear, colorless, almost 
odorless, slightly acid in reaction, with a specific gravity of 1.003 or 1-004. 

The total quantity of perspiration excreted daily has been estimated 
at about two pounds, though the amount varies with the nature of the food 
and drink, exercise, external temperature, season, etc. 

The elimination of the sweat is not intermittent, but continuous; 
but it takes place so gradually that as fast as it is formed it passes off by 
evaporation as insensible perspiration. Under exposure to great heat and 
exercise the evaporation is not sufficiently rapid, and it appears as sensible 
perspiration. 

COMPOSITION OF SWEAT. 

^ ater • 995-573 

Urea 0.043 

Fatty matters 0.014 

Alkaline lactates... °-3^7 

Alkaline sudorates 1.562 

Inorganic salts 2 .49 1 

iooo.ooo 



NERVOUS SYSTEM. 63 

Urea is a constant ingredient. 

Carbonic acid is also exhaled from the skin, the amount being about 
2^0 of that from the lungs. 

Perspiration regulates the temperature, and removes waste matters 
from the blood ; it is so important, that if elimination be prevented death 
occurs in a short time. 

The Nervous System influences the secretion of watery vapor by 
causing a dilatation of the capillary blood vessels around the tubular cpil. 
It is increased by mental emotions; section of the sympathetic fibres in 
the neck is followed by a copious perspiration ; stimulation of the nerves 
producing contraction of the vessels, is followed by an arrestation of the 
elimination of the sweat. 

NERVOUS SYSTEM. 

The Nervous System co-ordinates all the various organs and tissues 
of the body, and brings the individual into conscious relationship with 
external nature by means of sensation, motion, language, mental and moral 
manifestations. 

The Nervous Tissue may be divided into two systems, viz : the 
Cerebrospinal and the Sympathetic. 

(i) The Cerebro-spinal System occupies the cavities of the cranium 
and spinal canal, and consists of the brain, the spinal cord, the cranial and 
spinal nerves. It is the system of animal life, and presides over the func- 
tions of sensation, motion, etc. 

(2) The Sympathetic System, situated along each side of the spinal 
column, consists (1) of a double chain of ganglia, united together by 
nerve cords, which extends from the base of the cranium to the coccyx ; 
(2) of various ganglia, situated in the head and face, thorax, abdomen, 
pelvis, etc. All the ganglia are united together by numerous communi- 
cating fibres, many of which anastomose with the fibres of the cerebro- 
spinal system. It is the nervous system of organic life, and governs the 
functions of nutrition, growth, etc. 

Nervous Tissue is composed of two kinds of matter, the grey and 
white, which differ in their color, structure and physiological endowments ; 
the former consists of vesicles or cells which receive and generate nerve 
force ; the latter consists of fibres which simply conduct it, either from the 
periphery to the centre or the reverse. 

Structure of Grey Matter. It is found on the surface of the brain 
in the convolutions, in the interior of the spinal cord, and in the various 



64 HUMAN PHYSIOLOGY. 

ganglia of the cerebrospinal and sympathetic nervous systems. It is 
•composed of a fine connective tissue stroma, the neuroglia, in the 
meshes of which are embedded the grey cells or vesicles. 

The cells are greyish in color, and consist of a delicate investing cap- 
sule containing a soft, granular, albuminous matter, a nucleus, and some- 
times a nucleolus. Some of the cells are spherical or oval in shape, 
while others have an interrupted outline, on account of having one, two, 
or more processes issuing from them, constituting the unipolar, bi-polar y 
or multi-polar nerve cells. Cells vary in size ; the smallest being found in 
the brain, the largest in the anterior horns of grey matter of the spinal 
cord. 

Some of the cell processes become continuous with the fibres of the 
white matter, while others anastomose with those of adjoining cells and 
form a plexus. 

Structure, of the White Matter. Found for the most part in the 
interior of the brain, on the surface of the spinal cord, and in almost all of 
the nerves of the eerebro-spinal and sympathetic systems. 

It is composed of minute tubules or fibres, the ultimate nerve fibres, 
which, in the perfectly fresh condition, are apparently structureless and 
homogeneous ; but when carefully examined after death are seen to con- 
sist of three distinct portions, (i) a tubular membrane; (2) the white sub- 
stance of Schwann; (3) the axis cylinder. 

The tubular membrane, investing the nerve filament, is thin, homo- 
geneous, and lined by large oval nuclei, and presents, in its course, annu- 
lar constrictions ; it serves to keep the internal parts of the fibre in position, 
and protects them from injury. 

The white substance of Schwann, or the medullary layer, is situated 
immediately within the tubular membrane, and gives to the nerves their 
peculiar white and glistening appearance. It is composed of oleaginous 
matter in' a more or less fluid condition; after death it undergoes coagula- 
tion, giving to the fibre a knotted or varicose appearance. It serves to 
insulate the axis cylinder, and prevents the diffusion of the nerve force. 

The axis cylinder occupies the centre of the medullary substance. In 
the natural condition it is transparent and invisible, but when treated by 
proper reagents, it presents itself as a pale, granular, flattened band, albu- 
minous in character, more or less solid, and somewhat elastic. It is com- 
posed of a number of minute fibrillae united together to form a single 
bundle. (Schultze.) 

Nerve fibres in which these three structural elements coexist are known 
as the medullated nerve fibres. In the sympathetic system, and in the 



SPINAL NERVES. 65 

grey substance of the cerebro-spinal system, many nerves are destitute of 
a medullary layer, and are known as the non-medullated nerve fibres. 

Grey or Gelatinous nerve fibres, found principally in the sympathetic 
system, are grey in color, semi-transparent, flattened, with distinct borders, 
finely granular, and present oval nuclei. 

The diameter of the gelatinous fibres is about the -g-oVo^ 1 °^ an mcn '•> °f 
the medullated fibres, from 2 sVo^ to tto o tn °f an mcn - 

Ganglia are small bodies, varying considerably in size, situated on the 
posterior roots of spinal nerves, on the sensory cranial nerves, alongside 
of the vertebral column forming a connected chain, and in the different 
viscera. They consist of a dense, investing, fibrous membrane, containing 
in its interior grey or vesicular cells, among which are found white and 
gelatinous nerve-fibres. They may be regarded as independent nerve 
centres. 

Structure of Nerves. Nerves are rounded or flattened cords extend- 
ing from the centres to the periphery ; they are surrounded externally by 
a sheath, the neurilemma, composed of fibrous and elastic tissue forming 
a stroma, in which blood vessels ramify, which give to the nerves their 
nourishment. 

A nerve consists of a greater or less number of ultimate nerve filaments, 
separated into bundles by fibrous septa given off from the neurilemma. 
The nerve filaments pursue an uninterrupted course, from their origin to 
their termination; branches pass from one nefve trunk into the sheath of 
another, but there is no anastomosis or coalescence with adjoining nerve 
fibres. 

A plexus is formed by a number of branches of different nerves inter- 
lacing in every direction, in the most intricate manner, but from which 
fibres are again given off to pursue their independent course, e.g., brachial, 
cervical, lumbar, sacral, cardiac plexuses, etc. 

SPINAL NERVES. 

Origin. The spinal nerves are thirty-one (31) in number on each side 
of the spinal cord, and arise by two roots, an anterior and posterior, 
from the anterior and posterior aspects of the cord respectively ; the pos- 
terior roots present near their emergence from the cord a small ganglionic 
enlargement ; outside of the spinal canal the two roots unite to form a 
main trunk, which is ultimately distributed to the skin, muscles and 
viscera. 

The Function of the Anterior Roots is to transmit motor impulses 
from the centres outward to the periphery. 



66 HUMAN PHYSIOLOGY. 

Irritation of these roots, from whatever cause, excites convulsive move- 
ments in the muscles to which they are distributed ; division of the roots 
produces paralysis. 

The Function of the Posterior Roots is sensory, and transmits 
impressions made upon the periphery to the centres in the brain and 
spinal cord. Irritation of these roots gives rise to painful sensations ; 
division of the roots abolishes all sensation in the parts to which they are 
distributed. 

The ganglion on the posterior root influences the nutrition of the sen- 
sory nerve ; if the nerve be separated from the ganglion, it undergoes de- 
generation in the course of a few days. The nutrition of the anterior root 
is governed by nerve cells in the grey matter of the cord ; division of the 
nerve is followed by degeneration outward. * 

Nerve Terminations, (i) Peripheral. As the nerves approach the 
tissues to which they are to be distributed, they inosculate freely, fonning 
a plexus from which the ultimate fibres are sent to individual tissues. 

Motor Nerves. In the voluntary or striped muscles the motor nerves 
are connected with the contractile substance by means of the " motor ial 
end plates /" when the nerve enters the muscular fibre the tubular mem- 
brane blends with the sarcolemma, the medullary layer disappears, and the 
axis cylinder spreads out into the form of a little plate, granular in char- 
aracter, and containing oval nuclei. 

In the unstriped or involuntary muscles, the terminal nerve fibres form 
a plexus on the muscular fibre cells, and become connected with the 
granular contents of the nuclei. 

In the glands nerve fibres have been traced to the glandular cells, where 
they form a branching plexus from which fibres pass into their interior 
and become connected with their sub.-tance, and thus influence secretion. 

Sensitive Nerves terminate in the skin and mucous membranes in 
three distinct modes, e. g., as tactile corpuscles, Pacinian corpuscles, and 
as end bulbs. 

The tactile corpuscles are found in the papillae of the true skin, espe- 
cially on the palmar surface of the hands and fingers, feet and toes ; they 
are oblong bodies, measuring about g^th of an inch in length, consisting 
of a central bulb of homogeneous connective tissue surrounded by elastic 
fibres and elongated nuclei. The nerve fibre approaches the base of the 
corpuscle, makes two or three spiral turns around it, and terminates in loops. 
They are connected with the sense of touch. 

The Pacinian corpuscles are found chiefly in the subcutaneous cellular 
tissue, on the nerves of the hands and feet, the intercostal nerves, the 



PROPERTIES AND FUNCTIONS OF NERVES. 67 

cutaneous nerves, and in many other situations. They are oval in shape, 
measure about the ^th of an inch in length on the average, and consist 
of concentric layers of connective tissue ; the nerve fibre penetrates the 
corpuscle and terminates in a rounded knob in the central bulb. Their 
function is unknown. 

The e nd bulbs of Krause are formed of a capsule of connective tissue in 
which the nerve fibre terminates in a coiled mass or bulbous extremity ; 
they exist in the conjunctiva, tongue, glans penis, clitoris, etc. 

Many sensitive nerves terminate in the papillae at the base of the hair 
follicle ; but in the skin, mucous membranes, and organs of special sense 
their mode of termination is not well understood. 

(2) Central. Both motor and sensory nerve fibres, as they enter the 
spinal cord and brain, lose their external investments, and retain only the 
axis cylinder, which ultimately becomes connected with the processes of 
the grey cells. 

PROPERTIES AND FUNCTIONS OF NERVES. 

Classification. Nerves may be divided into two groups, viz : — 

(1) Afferent or centripetal, as when they convey to the nerve centres 
the impressions which are made upon their peripheral extremities or parts 
of their course. They may be sensitive, as w T hen they transmit impres- 
sions which give rise to sensations ; inhibitory, when they conduct im- 
pressions which produce a restraining or inhibiting action on a nerve 
centre ; reflective or excitant, when the impression carried to the nerve 
centre is reflected outward by an efferent nerve and produces motion or 
some other effect in the part to which the nerve is distributed. 

(2) Efferent or centrifugal, as when the impulses generated in the 
centres are transmitted outward to the muscles and various organs. They 
may be motor, as when they convey impulses to the voluntary and involun- 
tary muscles; vaso-motor, when they regulate the calibre of the small blood 
vessels, increasing or diminishing the amount of blood to a part ; secretory, 
when they influence secretion; trophic, when they influence nutrition. 

The rate of conduction of impressions is about the same in both sensi- 
tive and motor nerves, varying from 100 to 200 feet per second, according 
to the temperature, degree of excitability, etc. 

The axis cylinder is the essential conducting agent, the white substance 
of Schwann and tubular membrane being probably accessory struc- 
tures, protecting the axis from injury, and preventing the diffusion of 
nerve force to adjoining nerves. 

The properties of sensation and motion reside in different nerve fibres. 



68 HUMAN PHYSIOLOGY. 

Motor nerves can be destroyed or paralyzed by the introduction of 
woorara under the skin, without affecting sensation ; the sensibility of 
nerves can be abolished by the employment of anaesthetics without de- 
stroying motion. 

Irritability. Nerves conduct peripheral impressions to the centres, and 
motor impulses to the periphery, in virtue of their possessing an ultimate 
and inherent property, denominated neurility, nervous irritability, or 
excitability, which is manifested as long as the physical and chemical integ- 
rity of the nerve is maintained. 

Nerve degeneration. When nerves are separated from their trophic or 
nutritive centres they degenerate progressively in the direction in which 
they conduct impressions. In motor nerves, from the centre to the peri- 
phery ; in sensory nerves, from the periphery to the centres. 

Nerve force is not identical with electricity. Nerves do not possess the 
power of generating force within themselves, but act in response to chemi- 
cal, physical and mechanical stimuli from without, and to volitional acts, 
normal and pathological conditions, from within. 

Electrical Properties of Nerves. When a galvanic current is made 
to flow along a motor nerve from the centre to the periphery, it is known as 
the direct descending or centrifugal current ; when it is made to flow in 
the reverse direction, it becomes the inverse, ascending or centripetal current. 

If the current be feeble, neither muscular contraction nor pain is ordi- 
narily manifested during the actual passage of the current, whether direct 
or inverse ; but if the strength of the current be increased, or the excita- 
bility of the nerve be exalted, contraction is produced in the muscles at 
the moment the circuit is closed and again when it is broken. 

If the current be feeble, or the excitability be diminished, the contrac- 
tion of the muscle is produced only upon the closure of the circuit when 
the current is direct, and upon the breaking of the circuit when the cur- 
rent is inverse. 

The extent of muscular contraction is proportionate to ( I ) the strength 
of the current, and (2) to the extent of nerve included between the elec- 
trodes. Nervous excitability may be enfeebled or even exhausted by the 
continuous passage of the direct galvanic current; under these circum- 
stances, it may be restored by repose and the passage of the inverse 
current. 

The passage of a galvanic current through a portion of a nerve excites 
in the parts beyond the electrodes a condition of electric tension or elec- 
trotonus, during which the excitability is increased near the cathode or 
negative pole, and diminished near the anode or positive' pole, while 



NERVES OF SPECIAL SENSE. 69 

between the electrodes there is a neutral point at which the excitability is 
not affected. 

CRANIAL NERVES. 

The Cranial Nerves come off from the base of the brain, pass through 
the foramina in the walls of the cranium, and are distributed to the skin, 
muscles and organs of sense in the face and head. 

According to the classification of Soemmering, there are 12 pairs of 
nerves, enumerating them from before backwards, as follows, viz : — 
1st Pair, or Olfactory. 7th Pair, or Facial, Portio dura. 

2d Pair, or Optic. 8th Pair, or Auditory, Portio mollis. 

3d' Pair, or Motor oculi communis. 9th Pair, or Glosso-pharyngeal. 
4th Pair, or Patheticus, Trochlearis. 10th Pair, or Pneumogastric. 
5th Pair, or Trifacial, Trigeminus. 1 ith Pair, or Spinal accessory. 
6th Pair, or Abducens. 12th Pair, or Hypoglossal. 

The Cranial Nerves may be classified physiologically, according to 
their function, into three groups. 1. Nerves of special sense. 2. Nerves 
of motion. 3. Nerves of general sensibility. 

1. NERVES OF SPECIAL SENSE. 

1st Pair. Olfactory. 

Deep origin not satisfactorily determined. Apparent origin from the 
inferior and internal portion of the anterior lobes of the cerebrum by three 
roots, viz : an external white root, which passes across the fissure of 
Sylvius to the middle lobe of the cerebrum ; an internal white root from 
the most posterior part of the anterior lobe ; a grey root from the grey 
matter in the posterior and inner portion of the inferior surface of the 
anterior lobe. 

Distribution. To the olfactory mucous membrane ; the upper part of 
the Schneiderian mucous membrane, extending from the cribriform plate of 
the ethmoid bone downward nearly one inch. 

Function. Govern the sense of smell, but are insensible to ordinary 
impressions. 

2d Pair. Optic. 

Origin. An external white root from the anterior tubercle of the tuber- 
cula quadrigemina ; an internal white root from the posterior tubercle ; a 
grey root from the grey matter in the floor of the 3d ventricle. Filaments 
also come from the corpora geniculata and optic thalami and cerebral pe- 
duncles. 

Course of the Nerve. The two roots unite to form a flattened band, 



70 HUMAN PHYSIOLOGY. 

the optic tract, which winds around the eras cerebri to decussate with the 
nerve of the opposite side, forming the optic chiasm. The decussation of 
fibres is not complete ; some of the fibres of the left optic tract going to 
the outer half of the eye of the same side, and to the inner half of the 
eye of the opposite side ; the same holds true for the right optic tract. 

The optic nerves proper arise from the commissure, pass forward through 
the optic foramina, and are finally distributed in the retina. 

Properties of the Optic Nerves. They are insensible to ordinary 
impressions, and convey only the special i?npressions of light. 

Division of one of the nerves produces complete blindness in the eye 
of the corresponding side ; division of the optic tract produces loss of sight 
in the outer half oi the eye of the same side, and in the inner half of the 
eye of the opposite side. Lesion of the anterior part of the optic chiasni 
causes blindness in the inner half of the two eyes. 

Function. Govern the sense of sight. 

8th Pair, Portio-mollis, Auditory Nerve. 

Origin ; by two roots from the floor of the 4th ventricle, each root con- 
sisting of a number of grey filaments, some of which decussate in the 
median line ; the external root has a gangliform enlargement containing 
fusiform nerve cells. The two roots wind around the restiform bodies and 
enter the internal auditory meatus, and divide into an anterior branch dis- 
tributed to the cochlea, and a posterior branch distributed to the vestibule 
and semicircular canals. 

Properties of the Auditory Nerves. They are soft in consistence, 
greyish in color, consisting of axis cylinders with a medullary sheath only; 
they are not sensible to ordinary impressions, but convey the impression 
of sound. 

Function. Govern the sense of hearing. 

Chorda Tympani ; a branch of the Facial. 

Origin. From the facial nerve in the aqueduct of Fallopius ; it then passes 
through the tympanum between the ossicles of the ear, joins the inferior 
maxillary division of the 5th nerve at an acute angle between the ptery- 
goid muscles, and runs with the lingual branch, to be distributed to the 
mucous membrane of the anterior two-thirds of the tongue. 

Function. Governs the sense of taste, and is probably neither motor 
nor sensory. (See Facial nerve). 

Lingual Branches of the glosso-pharyngeal, or 9th pair, distributed 
to the posterior third of the tongue, endow it with the sense of taste. 
Probably connected with the papillae. 



NERVES OF MOTION. 71 

2. NERVES OF MOTION. 
3d Pair. Motor Oculi Communis. 

Origin. By filaments coming from the lenticular nucleus, corpora 
quadrigemina, optic thalamus ; these filaments converge to form a main 
trunk, which winds around the crus cerebri, in front of the pons Varolii. 

Distribution. The nerve then passes forward, and enters the orbit 
through the sphenoidal fissure, where it divides into a superior branch, 
distributed to the superior rectus and levator palpebrce muscles; an inferior 
branch sending branches to the internal and inferior recti, and the infe- 
rior oblique muscles ; filaments also pass into the ciliary ox ophthalmic gan- 
glion, from which the ciliary nerves arise, enter the eyeball, and are dis- 
tributed to the circular fibres of the iris and the ciliary muscle. The 3d 
nerve also receives filaments from the cavernous plexus of the sympathetic 
and from the 5th nerve. 

Properties. Irritation of the root of the nerve produces contraction 
of the pupil, internal strabismus, muscular movements of eye, but no 
pain. Section of the nerve produces ptosis, a falling of the upper eyelid, 
external strabismus, due to the unopposed action of the external rectus 
muscle ; dilatation of the pupil and persistent accommodation of the eye for 
long distances, from paralysis of the circular fibres of the iris and ciliary 
muscle : and inability to rotate the eye, slight protrusion and double vision, 
the images being on the same plane. 

Function. Governs movements of the eyeball by animating all the 
muscles except the external rectus and superior oblique, the movements of 
the iris, elevates the upper lid, influences the accommodation of the eye 
for distances. Can be called into action by (1) voluntary stimuli, (2) by 
reflex action through irritation of the optic nerve. 

4th Pair. Patheticus. 

Apparent origin from the superior peduncles of the cerebellum. 

Deep origin by fibres terminating in the corpora quadrigemina, lenticu- 
lar nucleus, valve of Vieussens, and in the substance of the cerebellar 
peduncles ; some filaments pass over the median line and decussate with 
fibres of the opposite side. 

Distribution. It enters the orbital cavity through the sphenoidal 
fissure, and is distributed to the superior oblique muscle ; in its course 
receives filaments from the ophthalmic branch of the 5th pair and the 
sympathetic. 

Properties. When the nerve is irritated muscular movements are pro- 



72 HUMAN PHYSIOLOGY. 

duced in the superior oblique muscle, and the pupil of the eye is turned down- 
ward and outward. Division or paralysis of the nerve renders the eye- 
ball immovable as far as rotation is concerned, and 'produces double 
vision. 

Function. Governs the movements of the eyeball produced by the 
action of the superior oblique muscles. 

5th Pair. Small Root. Nerve of Mastication. 

Apparent origin from the side of the pons Varolii. Deep origin by fila- 
ments going to the floor of the 4th ventricle, some of which decussate with 
those of the opposite side. 

Distribution. It passes forward from this origin, beneath the ganglion 
of Gasser, through the foramen ovale, and joins the inferior maxijlary 
division of the 5th nerve, which divides into two branches, anterior and 
posterior ; the.- former being distributed to the muscles of mastication, viz : 
temporal, masseter, external and internal pterygoid muscles. 

Properties. Galvanization of the nerve produces movements of the 
masticatory muscles. 

Section of the nerve causes paralysis of these muscles, and the jaw is 
turned to the opposite side by the action of the opposing muscles. 

Function. Stimulates the muscles which open and close the mouth 
and move the jaw from side to side during mastication, and assists deglu- 
tition by acting upon the muscles of the palate. 

6th Pair. Abducens. Motor Oculi Externus. 

. Deep origin is in the grey matter of the medulla oblongata. Apparent 
origin from the groove between the anterior pyramidal body and the pons 
Varolii, where it arises by two roots ; it then passes into the orbit through 
the sphenoidal fissure, and is distributed to the external recttis muscle. 
Receives filaments from the cervical portion of the sympathetic, through the 
carotid plexus and spheno-palatine ganglion, these being traced to the 
cilio-spinal centre in the spinal cord. 

Properties. When irritated, the external rectus muscle is thrown into 
convulsive movements, and the eyeball is turned outward. When divided 
or paralyzed, this muscle is paralyzed, and internal strabismus is produced. 

Function. To turn the eyeball outward. 

7th Pair. Portio-dura. Facial Nerve. 

Apparent origin, from the groove between the olivary and restiform 
bodies at the lateral portion of the medulla oblongata, and below the mar- 
gin of the pons Varolii. 



NERVES OF MOTION. To 

Deep origin. From a nucleus of large cells in the floor of the 4th ventricle 
below the nucleus of origin of the 6th pair, with which it is connected. 
Some filaments are traceable to the lenticular nucleus of the opposite side. 
Some of the fibres cross the median line and decussate. It is intimately- 
associated with the nerve of Wrisberg at its origin. 

Distribution. From its origin the facial nerve passes into the internal 
auditory meatus, and then, in company with the nerve of Wrisberg, enters 
the aqueduct of Fallopius. The filaments of the nerve of Wrisberg are 
supplied with a ganglion of a reddish color, having nerve cells. These 
filaments unite with those of the root of the facial, to form a common trunk, 
which emerges at the stylo-mastoid foramen. 

In the aqueduct the facial gives off the following branches, viz : — 

1. Large petrosal nerve, which passes forward to the spheno-palatine, 
or Meckel's ganglion, and through this to the levator palati and azygos 
uvulae muscles, which receive motor influence from this source. 

2. Small petrosal nerve, going to the otic ganglion and animating the 
tensoi'-tympani muscle. 

3. Tympanic branch, giving motion to the stapedius muscle. 

4. Chorda tyinpani, which joins the lingual branch of the 5th pair, and is 
distributed to the mucous membrane of the anterior two-thirds of the 
tongue ; it is the motor nerve of the sub-maxillary and parotid glands, and 
governs their secretions. 

After emerging from the stylo-mastoid foramen, it sends branches to the 
muscles of the ear, the occipito-frontalis, the digastric, the palato-glossi, 
and palato-pharyngei ; after which it passes through the parotid gland and 
divides into the temporo-facial and cervico- facial branches, distributed to 
the superficial muscles of the face, viz: occipito-frontalis, corrugator 
supercilii, orbicularis palpebrarum, levator labii superioris, et alseque nasi, 
buccinator, levator anguli oris, orbicularis oris, zygomatic, depressor anguli 
oris, etc. 

Properties. Undoubtedly a motor nerve at its origin, but in its course 
receives sensitive filaments from the 5th pair and the pneumogastric. 

Irritation of the nerve, after its emergence from the stylo-mastoid fora- 
men, produces convulsive movements in all the superficial muscles of the 
face. Division of the nerve at this point causes paralysis of these muscles 
on the side of the section, constituting facial paralysis; the phenomena of 
which are, a relaxed and immobile condition of the side of the face ; the 
eyelids remain open, from paralysis of the orbicularis palpebrarum ; the act 
of winking is abolished ; the angle of the mouth droops, and saliva con- 
stantly drains away; the face is drawn over to the sound side; face be- 



74 HUMAN PHYSIOLOGY. 

comes distorted upon talking or laughing;' mastication is interfered with, 
the food accumulating between the gums and cheek, from paralysis of the 
buccinator muscle ; fluids escape from the mouth in drinking ; articulation 
is impaired, the labial sounds being imperfectly pronounced. 

Properties of the branches given off in the aqueduct of Fallopius. The 
large petrosal, when irritated, throws the levator palati and azygos uvulae 
muscles into contraction. Paralysis of this nerve, from deep-seated lesions, 
produces a deviation of the uvula to the sound side, a drooping of the 
palate, and an inability to elevate it. 

The small petrosal influences hearing by animating the tensor tympani 
muscle ; when paralyzed, there occurs partial deafness and an increased 
sensibility to sonorous impressions. 

The tympanic branch animates the stapedius muscle, and influences 
audition. 

The chorda tympani controls the circulation, and the secretion 
of saliva, in the sub-maxillary glands, and governs the sense of taste. 
Galvanization of the chorda tympani dilates the blood vessels, increases 
the quantity and rapidity of the stream of blood, and increases the secre- 
tion of saliva. Division of the nerve is followed by contraction of the 
vessels, an arrestation of the secrelion, and a diminution of the sense of 
taste. 

Function. The facial is the nerve of expression, and co-ordinates the 
muscles employed to delineate the various emotions, influences the sense 
of taste, deglutition, movements of the uvula and soft palate, the tension 
of the membrana tympani, and the secretions of the sub maxillary and 
parotid glands. Indirectly influences smell, hearing and vision. 

11th Pair. Spinal Accessory. 

Apparent origin is by two sets of filaments : — 

1. A bulbar or medullary set, four or five in number, from the lateral or 
motor tract of the lower half of the medulla oblongata, below the origin of 
the pneumogastric. 

2. A spinal set, from 6 to 8 in number, from the lateral portion of the 
spinal cord, between the anterior and posterior roots of the upper four or 
five cervical nerves. 

Deep origin. The medullary portion arises in a nucleus in the lower 
half of the floor of the 4th ventricle, common to the pneumogastric and 
glbsso-pharyngeal nerves. The spinal portion has its origin in an elon- 
gated nucleus lying along the external surface of the anterior cornua of 
the spinal cord, extending down to the 5th cervical vertebra. 



NERVES OF MOTION. 75 

Distribution. From this origin the fibres unite to form a main trunk, 
which enters the cranial cavity through the foramen magnum, where it is 
at times joined by fibres from the posterior roots of the two upper cervical 
nerves, and sends filaments to the ganglion of the. root of the pneumo- 
gastric. After emerging from the cranial cavity through the jugular fora- 
men, it sends a branch to the pneumogastric, and receives others in return, 
and also from the 2d, 3d, and 4th cervical nerves. It divides into two 
branches: (1) An internal or anastomotic branch, made up of filaments 
coming principally from the medulla oblongata, and is distributed to the 
muscles of the pharynx through the pharyngeal nerves coming from the 
pneumogastric ; to all the muscles of the larynx, except the crico-thyroid, 
through the inferior laryngeal nerve ; to the heart, by filaments which 
reach it through the pneumogastric nerve. (2) An external branch, which 
is distributed to the sterno-cleido-mastoid and trapezius muscles ; these mus- 
cles also receiving filaments from the cervical nerves. 

Properties. At its origin it is a purely motor nerve, but in its course 
exhibits some sensibility from anastomosing fibres. 

Destj'uction of the medullary root, by tearing it from its attachment by 
means of forceps, impairs the action of the muscles of deglutition, and de- 
stroys the power of producing vocal sounds by paralysis of the laryngeal 
muscles, without, however, interfering with the respiratory movements of 
the larynx; these being controlled by other motor nerves. The normal 
rate of movement of the heart is also impaired by destruction of the medul- 
lary root. (See pneumogastric nerve.) 

Irritation of the external branch throws the trapezius and sterno-mastoid 
muscles into convulsive movements, though section of the nerve does not 
produce complete paralysis, as they are also supplied with motor influence 
from the cervical nerves. The sterno-mastoid and trapezius muscles per- 
form movements antagonistic to those of respiration, fixing the head, neck 
and upper part of the thorax, and delaying the expiratory movement 
during the acts of pushing, pulling, straining, etc.; and in the production 
of a prolonged vocal sound, as in singing. When the external branch 
alone is divided, in animals, they experience shortness of breath during 
exercise, from a want of coordination of the muscles of the limbs and res- 
piration; and while they can make a vocal sound, it cannot be prolonged. 
Function, Governs phonation by its influence upon the vocal move- 
ments of the glottis; influences the movements of deglutition, the action of 
the heart, and certain respiratory movements associated with sustained or 
prolonged muscular efforts and phonation. 



76 HUMAN PHYSIOLOGY. 

12th Pair. Hypoglossal or Sublingual. 

Apparent origin, by two groups of filaments from the medulla oblongata, 
in the groove between the olivary body and the anterior pyramid. 

Deep origin ; from the hypoglossal nucleus situated deeply in the sub- 
stance of the medulla on a level with the lowest portion of the floor of 
the 4th ventricle ; some decussating filaments have been traced to a higher 
encephalic centre. 

Distribution. The trunk formed by the union of the root filaments, 
passes out of the cranial cavity through the anterior condyloid foramen, 
occasionally receiving a filament from the lateral and posterior portion of 
the medulla oblongata. After emerging from the cranium, it sends fila- 
ments to the sympathetic and pneumogastric ; it anastomoses with the 
lingual branch of the 5th pair, and receives and sends filaments to the 
upper cervical nerves. The nerve is finally distributed to the sterno-hyoid, 
sterno-thyroid, omo-hyoid, thyrohyoid, stylo-glossi, hyo-glossi, genio-hyoid, 
genio-hyo-glossi, and the intrinsic muscles of the tongue. 

Properties. A purely motor nerve at its origin, but derives sensibility 
outside of the cranial cavity, from anastomosis with the cervical, pneumo- 
gastric and 5th nerves. 

Irritation of the nerve gives rise to convulsive movements of the 
tongue and slight evidences of sensibility. 

Division of the nerve abolishes all movement of the tongue and inter- 
feres considerably with the act of deglutition. 

When the hypoglossal nerve is involved in hemiplegia, the tip of the 
tongue is directed to the paralyzed side when the tongue is protruded ; 
due to the unopposed action of the genio-hyo-glossus of the sound side. 

Articulation is considerably impaired in paralysis of this nerve ; great 
difficulty being experienced in the pronunciation of the consonantal 
sounds. 

Mastication is performed with difficulty, from inability to retain the 
food between the teeth until it is completely triturated. 

Function. Governs all the movements of the tongue and influences 
the functions of mastication, deglutition and articulate language. 

3. NERVES OF GENERAL SENSIBILITY. 

5th Pair. Trifacial. Trigeminal (Large Root). 

Apparently originates from the side of the pons Varolii. 
The deep origin is from the upper part of the floor and anterior wall of 
the 4th ventricle, by three bundles of filaments, one of which anastomoses 



.NERVES OF GENERAL SENSIBILITY. 77 

with the auditory nerve ; another passes to the lateral tract of the medul- 
la ; while a third, greyish in color, goes to the restiform bodies, and may 
be traced to the point of the calamus scriptorius. 

Filaments of origin have been traced to the " trigeminal sensory nu- 
cleus," located on a level with the point of exit of the nerve; to the pos- 
terior grey horns of the cord, as low down as the middle of the neck. 

Distribution. The trunk of the nerve, formed by the union of these 
filaments, passes obliquely upward and forward to the ganglion of Gasser, 
which receives filaments of communication from the carotid plexus of the 
sympathetic. It then divides into three branches. 

1. Ophthalmic branch, which receives communicating filaments from 
the sympathetic, and sends sensitive fibres to all the motor nerves of the 
eyeball. 

It is distribute d\.o> the ciliary ganglion, lachrymal gland, sac, and caruncle, 
conjunctiva, integument of the upper eyelid, forehead, side of head and 
nose, anterior portion of the scalp, ciliary muscle and iris. 

2. Superior maxillary branch, sends branches to the spheno-palatine 
ganglion, integument of the temple and lower eyelid, side of forehead, 
nose, cheek and upper lip, teeth of the upper jaw, and alveolar processes. 

3. Inferior maxillary branch, which, after receiving in its course fila- 
ments from the small root and from the facial, is distributed to the sub- 
maxillary ganglion, the parotid and sub-lingual glands, external auditory 
meatus, mucous membrane of the mouth, anterior two-thirds of the tongue 
(lingual branch), gums, arches of the palate, teeth of the lower jaw, and 
integument of the lower part of the face. 

Properties. It is the most acutely sensitive nerve in the body, and 
endows all the parts to which it is distributed with general sensibility. 

Irritation of the main trunk, or any of its branches, will give rise to 
marked evidences of pain ; the various forms of neuralgia of the head and 
face being occasioned by compression, disease, or exposure of some of 
its terminal branches. 

Division of the nerve within the cranium is followed at once by a com- 
plete abolition of all sensibility in the head and face, but is not attended 
by any loss of motion. The integument, mucous membranes and the eye, 
may be lacerated, cut or bruised, without the animal exhibiting any evi- 
dence of pain. At the same time the lachrymal secretion is diminished, 
the pupil becomes contracted, the eyeball is protruded, and the sensibility 
of the tongue is abolished. 

The reflex movements of deglutition are also somewhat impaired; the 



78 HUMAN PHYSIOLOGY. 

impression of the food being unable to reach and excite the nerve centre 
in the medulla oblongata. 

Influence upon the Special Senses. After division of the large 
root within the cranium, a disturbance in the nutrition of the special 
senses sooner or later manifests itself. 

Sight. In the course of 24 hours the eye becomes very vascular and 
inflamed, the cornea becomes opaque and ulcerates, the humors are 
discharged, and the eye is totally destroyed. 

Smell. The nasal mucous membrane swells up, becomes fungous, and 
is liable to bleed on the slightest irritation. The mucus is increased in 
amount, so as to obstruct the nasal passages ; the sense of smell is finally 
abolished. 

Hearing, at times, is impaired, from disorders of nutrition in the middle 
ear and external auditory meatus. 

Alteration in the nutrition of the special senses is not marked if the sec- 
tion is made posterior to the ganglion of Gasser, and the anastomosing 
filaments of the sympathetic which join the nerve at this point; but if the 
ganglion be divided, these effects are very noticeable; due to the section of 
the sympathetic filaments. 

Function. Gives sensibility to all parts of the head and face to which 
it is distributed, and through fibres from the sympathetic governs the nutri- 
tion of the special senses. 

9th Pair. Glosso-Pharyngeal. 

Has two ganglia ; the jugular ganglion includes only a portion of the 
root filaments; the ganglion of Andersch includes all the fibres of the 
trunk. 

Apparent origin; partly from the medulla oblongata and the inferior 
peduncles of the cerebellum. 

Deep origin ; from the lower portion of the grey substance in the floor of 
the 4th ventricle. 

Distribution. The trunk of the nerve then passes downward and for- 
ward, receiving near the ganglion of Andersch fibres from the facial and 
pneumogastric nerves. It divides into two large branches, one of which 
is distributed to the base of the tongue, the other to the pharynx. In its 
course it sends filaments to the otic ganglion ; a tympanic branch, which 
gives sensibility to the mucous membrane of the fenestra rotunda, fenestra 
ovalis, and Eustachian tube ; lingual branches to the base of the tongue ; 
palatal branches to the soft palate, uvula and tonsils; pharyngeal branches 
to the mucous membrane of the pharynx. 



NERVES OF GENERAL SENSIBILITY. 79 

Properties. Irritation of the roots at their origin calls forth evidences 
of pain ; it is, therefore, a sensory nerve, but its sensibility is not so acute 
as that of the tri-facial. Irritation of the trunk after its exit from the 
cranium produces contraction of the muscles of the palate and pharynx, 
due to the presence of anastomosing motor fibres. 

Division of the nerve abolishes sensibility in the structures to which it 
is distributed, and impairs the sense of taste in the posterior third of the 
tongue (see sense of taste). 

Function. Governs sensibility of pharynx, presides partly over the 
sense of taste, and controls reflex movements of deglutition and vomiting. 

10th Pair. Pneumogastric. Par Vagum. 

Possesses two ganglia ; one in the jugular foramen, called the ganglion of 
the root, and another outside of the cranial cavity on the trunk, the gan- 
glion of the trunk. 

Apparent origin; from the lateral side of the medulla oblongata, just 
behind the olivary body. 

Deep origin; in the grey nuclei in the lower half of the floor of the 4th 
ventricle and in the substance of the restiform body. Some filaments are 
traced along the restiform tract, toward the cerebellum, and others to the 
median line of the floor of the 4th ventricle, where many of them decussate. 

Distribution. The filaments from the root unite to form a single trunk, 
which leaves the cavity of the cranium, through the jugular foramen, in 
company with the spinal accessory and glosso -pharyngeal. It soon re- 
ceives an anastomotic branch from the spinal accessory, and afterward 
branches from the facial, the hypoglossal and the anterior branches of the 
two upper cervical nerves. 

Properties. At its origin the pneumogastric nerve is sensory, as shown 
by direct irritation or galvanization, though its sensibility is not very 
marked. In its course exhibits motor properties from anastomosis with 
motor nerves. 

As the nerve passes down the neck it sends off the following main 
branches. 

1. Pharyngeal nerves, which assist in forming the pharyngeal plexus, 
which is distributed to the mucous membrane and muscles of the pharynx. 

2. Superior laryngeal nerve. Enters the Lirynx through the thyro- 
' hyoid membrane, and is distributed to the mucous membrane lining the 

interior of the larynx, and to the crico-thyroid muscle and the inferior 
constrictor of the pharynx. The "depressor nerve" found in the rabbit, 
is formed by the union of two branches, one from the superior laryngeal, 



80 HUMAN PHYSIOLOGY. 

the other from the main trunk; it passes- downward to be distributed to 
the heart. 

3. Inferior laryngeal. Sends its ultimate branches to all the intrinsic 
muscles of the larynx except the crico-thyroid, and to the inferior constric- 
tor of the pharynx. 

4. Cardiac branches, given off from the nerve throughout its course, unite 
with the sympathetic fibres "to form the cardiac plexus, to be distributed to 
the heart. 

5. Pulmonary branches, which form a plexus of nerves and are dis- 
tributed to the bronchi and their ultimate terminations, the lobules and 
air cells. 

From the right pneumogastric nerve branches are distributed to the 
mucous membrane and muscular coats of the stomach and intestines, to 
the liver, spleen, kidneys, and supra-renal capsules. 

The pharyngeal branches assist in giving sensibility to the mucous mem- 
brane of the pharynx, and influence reflex phenomena of deglutition, through 
motor fibres which they contain, derived from the spinal accessory. 

The superior la?yngeal nerve endows the upper portion of the larynx 
with sensibility ; protects it from the entrance of foreign bodies ; by con- 
ducting impressions to the medulla, excites the reflex movements of deglu- 
tition and of respiration; through the motor filaments it contains, produces 
contraction of the crico-thyroid muscle. 

Division of the " depressor nerve" and galvanization of the central end, 
retards and even arrests the pulsations of the heart and diminishes the 
pressure of blood in the large vessels, by causing dilatation of the intestinal 
vessels by reflex action through the splanchnic nerves. 

The inferior laryngeal contains, for the most part, motor fibres from 
the spinal accessory. When irritated, produces movement in the laryn- 
geal muscles. When divided, is followed by paralysis of these muscles, 
except the crico-thyroid, impairment of phonation, and an embarrassment of 
the respiratory movements of the larynx, and finally death, from suffocation. 

The cardiac branches, through filaments derived from the spinal acces- 
sory, exert a direct inhibitory action upon the heart. Division of the 
pneumogastrics in the neck increases the frequency of the heart's action. 
Galvanization of the peripheral ends diminishes the heart's pulsations, and 
finally paralyzes it in diastole. 

The pulmonary branches give sensibility to the bronchial mucous mem- 
brane, and govern the movements of respiration. Division of both 
pneumogastrics in the neck diminishes the frequency of the respiratory 
movements, falling as low as 4 to 6 per minute ; death usually occurs in 



CEREBRO-SPINAL AXIS. 81 

from 5 to 8 days. Feeble galvanization of the central ends of the divided 
nerves accelerates respiration; powerful galvanization retards, and may 
even arrest, the respiratory movements. 

The gastric branches give sensibility to the mucous coat, and through 
sympathetic filaments, which join the pneumogastrics high up in the neck, 
give motion to the muscular coat of the stomach. They influence the 
secretion of gastric juice, aid the process of digestion and absorption from 
the stomach. 

The hepatic branches , probably through anastomosing sympathetic fila- 
ments, influence the secretion of bile, and the glycogenic function of the 
liver ; division of the pneumogastrics in the neck produces congestion of 
the liver, diminishes the density of the bile, and arrests the glycogenic 
function ; galvanization of the central ends exaggerates the glycogenic 
function, and makes the animal diabetic. 

The intestinal branches give sensibility and motion to the small intestines, 
and when divided, purgatives generally fail to produce purgation. 

Function. A great sensitive nerve which, through anastomotic fila- 
ments from motor sources influences deglutition, the action of the heart, 
the circulatory and respiratory systems, voice, the secretions of the stom- 
ach, intestines, and various glandular organs. 

CEREBRO-SPINAL AXIS. 

The Cerebro-Spinal Axis consists of the spinal cord, medulla oblon- 
gata, pons Varolii, cerebellum and cerebrum, exclusive of the spinal and 
cranial nerves. It is contained within the cavities of the cranium and 
spinal column, and surrounded by three membranes, the dura mater, 
arachnoid and pia-mater, which protect it from injury and supply it with 
blood vessels. 

The Brain and Spinal Cord are composed of both white fibres and 
collections of grey cells, and are therefore to be regarded as conductors of 
impressions and motor impulses, as well as generators of nerve force. 
MEMBRANES. 

The Dura Mater, the most external of the three, is a tough membrane, 
composed of white fibrous tissue, arranged in bundles, which interlace in 
every direction. In the cranial cavity it lines the inner surface of the 
bones, and is attached to the edge of the foramen magnum ; sends pro- 
cesses inward, forming the falx cerebri, falx cerebelli, and tentorium cere- 
belli, supporting and protecting parts of the brain. In the spinal canal it 
loosely invests the cord, and is separated from the walls of the canal by 
areolar tissue. 



82 HUMAN PHYSIOLOGY. 

The Arachnoid, the middle membrane, is a delicate serous structure 
which envelopes the brain and cord, forming the visceral layer, and is 
then reflected to the inner surface of the dura mater, forming the pa?Hetal 
layer. Between the two layers there is a small quantity of fluid which 
prevents friction by lubricating the two surfaces. . 

The Pia Mater, the most internal of the three, composed of areolar 
tissue and blood vessels, covers the entire surface of the brain and cord, to 
which it is closely adherent, dipping down between the convolutions and 
fissures. 

It is exceedingly vascular, sending small blood vessels some distance 
into the brain and cord. 

The Cerebro-Spinal Fluid occupies the sub-arachnoid space, and the 
general ventricular cavity of the brain, which communicate by an opening, 
the foramen of Magendie, in the pia-mater, at the lower portion of the 4th 
ventricle. This fluid is clear, transparent, alkaline, possesses a salt taste, and 
a low specific gravity ; it is composed largely of water, traces of albumen, 
glucose and mineral salts. It is secreted by the pia-mater; the quantity 
is estimated from 2 to 4 fluid oz. 

The function of the cerebro-spinal fluid is to protect the brain and cord, 
by preventing concussion from without ; by being easily displaced into the 
spinal canal, prevents undue pressure and insufficiency of blood to the 
brain. (Kirke.) 

SPINAL CORD. 

The Spinal Cord varies from 16 to 18 inches in length; is half an inch 
in thickness, weighs 1^ oz., and extends from the atlas to the 2d lumbar 
vertebra, terminating in the filum terminale. It is cylindrical in shape, 
and presents an enlargement in the lower cervical and lower dorsal 
regions, corresponding to the origin of the nerves which are distributed to 
the upper and lower extremities. The cord is divided into two lateral 
halves by the anterior and posterior fissures. It is composed of both white 
ox fibrous and grey or vesicular matter, the former occupying the exterior 
of the cord, the latter the interior, where it is arranged in the form of two 
crescents, one in each lateral half, united together by a central mass, the 
grey commissure ; the white matter being united in front by the white 
commissure. 

Arrangement of the White Matter. Each lateral half of the cord 
is made up of nerve fibres, some of which are continuations of the nerves 
which enter the cord, while others are derived from different sources; it is 
subdivided into : (1) an anterior column, comprising that portion between 



SPINAL CORD. 83 

the anterior roots and the anterior fissure, (2) a lateral column, the por- 
tion between the anterior and posterior roots, (3) the posterior columns, 
the portion included between the posterior roots and the posterior fissure. 

Structure of the Grey Matter. The grey matter, arranged in the 
form of two crescents, presents an anterior and posterior horn. It is made 
up of a delicate network of fine nerve fibres (axis cylinders), supported 
by a connective tissue framework, nucleated nerve cells, which in the ante- 
rior horns are large and multipolar, and connected with the anterior roots 
of spinal nerves ; in the posterior horns the nerve cells are smaller, and 
situated along the inner margin, and in the caput cornu. Small cells are 
also found in the posterior vesicular columns, and in the intermediary 
lateral tract. 

COURSE OF THE ANTERIOR AND POSTERIOR ROOTS. 

The Anterior Roots pass through the anterior columns, horizontally, 
in straight and distinct bundles, and enter the anterior cornua, where they 
diverge in four directions. (1) Many become connected with the pro- 
longations of the multipolar nerve cells. (2) Others leave the grey mat- 
ter, pass through the anterior white commissure, and enter the anterior 
columns of the opposite side. (3) A considerable number enter the lateral 
columns of the same side, through which they pass to the medulla oblon- 
gata, where they decussate and finally terminate in the corpus striatum of 
the opposite side: (4) Others traverse the grey matter horizontally, and 
come into relation with the posterior roots. 

The Posterior Roots enter the posterior horns of the grey matter (1) 
through the substantia gelatinosa, (2) by the inner side ; of the. former, 
some bend upward and downward, and become connected with the ante- 
rior cornua ; others pass through the posterior commissure to the opposite 
side ; of the latter, fibres pass into the grey matter, to the posterior 
vesicular columns, passing obliquely through the posterior white columns 
upward and downward for some distance, and enter the grey matter at 
different heights. 

The posterior roots, in all probability, contain filaments which are con- 
ductors of the sensations of pain, touch, tickling and temperature. (For 
functions of anterior and posterior roots see page 65). 

Decussation of Motor and Sensory Fibres. The motor fibres 
which convey volitional impulses from the brain outward undergo almost 
complete decussation in the anterior pyramids of the medulla oblongata, 
and to a slight extent in the upper part of the cervical region, so that one 
half of the brain governs the muscular movements of the opposite half of 
the body. 



84 HUMAN PHYSIOLOGY. 

The sensory fibres, which convey impressions, made upon the periphery, 
to the cord and brain, undergo decussation at once upon entering the grey 
matter, throughout its entire length. 

Properties of the Spinal Cord. Irritation applied directly to the 
antero-lateral white columns produces muscular movements but no pain ; 
they are, therefore, excitable but insensible. 

The surface of the posterior columns is very sensitive to direct irritation, 
especially near the origin of the posterior roots ; less so toward the pos- 
terior median fissure. The sensibility is due, however, not to its own 
proper fibres, but to the fibres of the posterior roots which traverse it. 

Division of the antero-lateral columns abolishes all power of voluntary 
movement in the lower extremities. 

Division of the posterior columns impairs the power of muscular codrdi- 
nation, such as is witnessed in locomotor ataxia. 

The grey matter is probably both insensible and inexcitable under the in- 
fluence of direct stimulation. 

A transverse section of one lateral half of the cord produces : — 

(i) On the same side, paralysis of voluntary motion and a .relative or 
absolute elevation of temperature and an increased flow of blood in the 
paralyzed parts ; hyperesthesia for the sense of contact, tickling, pain and 
temperature. 

(2) On the opposite side complete anaesthesia as regards contact, pain, 
tickling and temperature, in the parts corresponding to those which are 
paralyzed in the opposite side. Complete preservation of voluntary power 
and of the muscular sense. 

A vertical section through the middle of the grey matter results in the loss 
of sensation on both sides of the body below the section, but no loss of 
voluntary power. 

FUNCTIONS OF THE SPINAL CORD. 

i. As a conductor. The lateral columns, particularly the posterior 
portions, the "pyramidal tracts," composed chiefly of longitudinally run- 
ning fibres, are the conductors of the voluntary motor impulses from the 
brain to the large multipolar nerve cells in the anterior cornua of grey 
matter, and through them become connected with the anterior roots which 
transmit the motor stimuli to the muscles. Division of the lateral columns, 
or secondary degeneration, results in paralysis of voluntary movement in 
the lower extremities. 

The anterior columns, especially the portion surrounding the anterior 
cornuae, the " anterior radicular zones," are composed of short longitudinal 



FUNCTIONS OF THE SPINAL CORD. 85 

commissural fibres, which serve to connect together different segments of the 
spinal cord ; the inner portions bordering the anterior median fissure, the 
columns of Tiirck, extend down as far as the middle of the dorsal region ; 
they are known as the direct pyramidal tracts, and convey motor stimuli 
to the grey horns. In cases of secondary degenerations from cerebral dis- 
ease, followed by paralysis of motion, these columns are frequently affected 
in connection with the lateral columns. 

The postei'ior columns are subdivided into the columns of Burdach, that 
portion lying next to the posterior horns, and the columns of Goll, the por- 
tion bordering the posterior median fissure. They are composed of short 
and long commissural fibres, and connect together different segments of the 
cord. They are insensible to direct irritation, but aid in the coordination 
of muscular movements in walking, standing, running, etc. Degeneration 
of the posterior columns gives rise to the lack of muscular coordination 
observed in locomotor ataxia. 

The Grey Matter. Sensitive impressions are conveyed from the peri- 
phery into the cord by the posterior roots of spinal nerves, and up to the 
brain, exclusively by the grey matter, and especially by that portion im- 
mediately surrounding the central canal. Decussation of the sensory 
fibres takes place throughout the whole length of the grey matter. 

The anterior cornuce of the grey matter are connected with the gener- 
ation and transmission of motor impulses outward, and are the trophic 
centres which govern the nutrition of the anterior roots of spinal nerves. 
Atrophy of the motor cells is followed by a paralysis of motion, degenera- 
tion of the anterior roots, and a subsequent atrophy of the muscles and 
bones. 

2. As an Independent Nerve Centre. 

The spinal cord, by virtue of its containing ganglionic nerve matter, is 
capable of transforming impressions made upon the centripetal nerves 
into motor impulses, which are reflected outward through centrifugal nerves 
to muscles, producing movements. These reflex movements taking place 
through the grey matter, are independent of sensation and volition. 

The reflex excitability is increased by the separation of the cord from 
the brain, the latter apparently exerting an inhibitory influence over the for- 
mer, and modifying its reflex movements. Strychnia also increases the 
excitability, producing involuntary contractions. 

All movements taking place through the nervous system are of this 
reflex character, and may be divided into excito-motor, sensori-motor, and 
ideo-motor. 



86 HUMAN PHYSIOLOGY. 

Classification of Reflex Movements. (Kiiss.) They may be divided 
into four groups, according to the route through which the centripetal 
and centrifugal impulses pass. 

1. Those normal reflex acts, e. g., deglutition, coughing, sneezing, walk- 
ing, etc., pathological reflex acts, e. g., tetanus, vomiting, epilepsy, w r hich 
take place both centripetally and centrifugally, through spinal nerves. 

2. Reflex acts which take place in a centripetal direction through a 
cerebro-spinal sensory nerve, and in a centrifugal direction through a sym- 
pathetic motor nerve, usually a vaso-motor nerve, e. g., the normal reflex 
acts which give rise to most of the secretions, pallor and blushing of the 
skin, certain movements of the iris, certain modifications in the beat of the 
heart ; the pathological, which, on account of the difficulty in explaining 
their production are termed metastatic, e. g., ophthalmia, coryza, orchitis, 
which depend on a reflex hyperaemia ; amaurosis, paralysis, paraplegia, 
etc., due to a reflex anaemia. 

3. Reflex movements, in which the centripetal impulse passes through a 
sympathetic nerve, and the centrifugal through a cerebro-spinal nerve ; 
most of these phenomena are pathological, e. g., convulsions from intes- 
tinal irritation produced by the presence of worms, eclampsia, hysteria, 
etc. 

4. Reflex actions in which both the centripetal and centrifugal impulses 
pass through filaments of the sympathetic nervous system, e. g., those ob- 
scure reflex actions which preside over the secretions of the intestinal fluids, 
which unite the phenomena of the generative organs, the dilatation of the 
pupils from intestinal irritation (worms), and many pathological phenomena. 

Laws of Reflex Action. (Pfluger.) 

1. Law of Unilaterality. If a feeble irritation be applied to one or 
more sensory nerves, movement takes place usually on one side only, and 
that upon the same side as the irritation. 

2. Law of Symmetry. If the irritation becomes sufficiently intense, 
motor reaction is manifested, in addition, in corresponding muscles of the 
opposite side of the body. 

3. Lazv of Lntensity. Reflex movements are usually more intense on 
the side of the irritation ; at times the movements of the opposite side equal 
them in intensity, but they are usually less pronounced. 

4. Law of Radiation, If the excitation still continues to increase, it is 
propagated upward, and motor reaction takes place through centrifugal 
nerves coming from segments of the cord higher up. 

5. Lazv of Generalization. When the irritation becomes very intense, 
it is propagated to the medulla oblongata ; motor reaction then becomes gen- 



FUNCTIONS OF THE SPINAL CORD. Of 

eral, and is propagated up and down the cord, so that all the muscles of 
the body are thrown into action, the medulla oblongata acting as a focus 
whence radiate all reflex movements. 

Special Centres in the Spinal Cord. 

Genito-spinal centre. In the lower portion of the spinal cord are 
located the centres which control the sphincter muscles of the rectum and 
bladder, the erection of the penis, the emission of the semen, the action 
of the uterus during parturition, etc. 

The cilio-spinal centre is situated in the spinal, cord between the 6th 
cervical and 2d dorsal nerves ; stimulation of the cord in this situation pro- 
duces a dilatation of both pupils through filaments of the sympathetic, 
which have their origin from this region of the cord. 

Paralysis from Disease of the Spinal Cord. 

Seat of lesion. If it be in the lower part of the sacral canal, there is 
paralysis of the compressor urethra, accelerator urinae, and sphincter ani 
muscles ; no paralysis of the muscles of the leg. 

At the upper limit of the sacral region. Paralysis of the muscles of the 
bladder, rectum and anus ; loss of sensation and motion in the muscles of 
the legs, except those supplied by the anterior crural and obturator, viz : 
psoas iliacus, Sartorius, pectineus, adductor longus, magnus- and brevis, 
obturator, vastus externus and internus, etc. 

At the tipper limit of the lumbar region. Sensation and motion para- 
lyzed in both legs ; loss of power over the rectum and bladder ; paralysis 
of the muscular walls of the abdomen interfering with expiratory movements. 

At the lower portion of the cervical region. Paralysis of the legs, etc., 
as above; in addition, paralysis of all the intercostal muscles and conse- 
quent interference with inspiratory movements; paralysis of muscles of 
the upper extremities, except those of the shoulders. 

Above the middle of the cervical region. In addition to the preceding, 
difficulty in deglutition and vocalization, contraction of the pupils, paraly- 
sis of the diaphragm, scalene muscles, intercostals, and many of the ac- 
cessory respiratory muscles; death resulting immediately, from arrest of 
respiratory movements. 

Anterior half of spinal cord. Paraplegia developing symmetrically. 

Posterior half of spinal cord. Characteristic symptoms of locomotor 
ataxia or tabes dorsalis. 

In the grey substance in the vicinity of the central canal and anterior 
horns. If the lesion be acute, symptoms characteristic of acute spinal 
paralysis manifest themselves ; if chronic, symptoms characteristic of pro- 
gressive muscular atrophy. 



88 HUMAN PHYSIOLOGY. 

MEDULLA OBLONGATA. 

The Medulla Oblongata, pyramidal in form, is the expanded por- 
tion of the upper part of the spinal cord It is one and a half inches 
in length, three-quarters of an inch in breadth, half an inch in thickness, 
and divided into two lateral halves by the anterior and posterior median 
fissures, continuous with those of the cord. Each half is again subdivided 
by minor grooves, into four columns, viz: anterior pyramid, lateral tract 
and olivary body, restiform body and posterior pyramid. 

1. The anterior pyramid is composed partly of fibres continuous with 
those of the anterior column of the spinal cord ; but mainly of fibres 
derived from the lateral tract of the opposite side, by decussation. The 
united fibres then pass upward through the pons Varolii and crura cerebri, 
and for the most part terminate in the corpus striatum and cerebrum. « 

2. The lateral tract is continuous with the lateral columns of the cord ; 
its fibres in passing upwards take three directions, viz : an external bundle 
joins the restiform body, and passes into the cerebellum ; an internal 
bundle decussates at the median line and joins the opposite anterior pyra- 
mid ; a middle bundle ascends beneath the olivary body, behind the pons, 
to the cerebrum, as the fasciculus teres. 

The olivary body of each side is an oval mass, situated between the 
anterior pyramid and restiform body ; it is composed of white matter ex- 
ternally, and grey matter internally, forming the corpus dentatum. 

3. The restiform body continuous with the posterior column of the cord, 
also receives fibres from the lateral column. As the restiform bodies pass 
upward they diverge and form a space, the 4th ventricle, the floor of which 
is formed by grey matter, and then turn backward and enter the cerebellum. 

4. The posterior pyramid is a narrow, white cord bordering the posterior 
median fissure ; it is continued upward in connection with the fasciculus 
teres, to the cerebrum. 

The Grey Matter of the medulla is continuous with that of the cord, 
but is arranged with much less regularity, becoming blended with the 
white matter of the different columns, except the anterior. By the separa- 
tion of the posterior columns, the transverse commissure is exposed, form- 
ing part of the floor of the 4th ventricle; special collections of grey matter 
are found in the posterior portions of the medulla, connected with the roots 
of origin of different cranial nerves. 

Properties and Functions. The medulla is excitable anteriorly, 
and sensitive posteriorly to direct irritation. It serves (1) as a conductor 
of sensitive impressions upwards from the cord through the grey matter to 



or 

Centripetal 
Nerves. 



Motor 

or 

Centrifugal 

Nerves. 



MEDULLA OBLONGATA. 89 

the cerebrum ; (2) as a conductor of voluntary impulses from the brain to 
the spinal cord and nerves through its anterior pyramids ; (3) a conductor 
of coordinating impulses from the cerebellum through the restiform bodies 
to the spinal cord. 

As an Independent Reflex Centre. The medulla oblongata contains 
special collections of grey matter, constituting independent nerve centres 
which preside over different functions, some of which are as follows, viz : — 

1. A centre which controls the movements of mastication through affer- 
ent and efferent nerves. 

2. A centre reflecting impressions which influence the secretion of saliva. 

3. A centre for deglutition, whence are derived motor stimuli exciting to 
action and coordinating the muscles of the palate, pharynx and oesophagus, 
necessary for the swallowing of the food. 

NERVOUS CIRCLE OF DEGLUTITION, (*d and 3d Stages.) 

Excitor * Palatal branches of 5th pair. 

Pharyngeal branches of the glosso-pharyngeal. 
Superior laryngeal branches of the pneumogastric. 
(^Esophageal branches of the pneumogastric. 
Pharyngeal branches of the pneumogastric, derived 

from the spinal accessory. 
Hypoglossal and branches of the cervical plexus. 
Inferior or recurrent laryngeal. 
Motor filaments of the 3d division of the 5th pair, 

Portio dura. 

4. A centre which coordinates the muscles concerned in the act of 
-vomiting. 

5. A speech centre, coordinating the various muscles necessary for the 
accomplishment of articulation through the hypoglossal, facial nerves and 
the 3d division of the 5th pair. 

6. A centre for the harmonization of muscles concerned in expression, 
through the facial nerve. 

7. A cardiac centre, which exerts (1) an accelerating influence over the 
heart's pulsations through accelerating nerve fibres emerging from the cer- 
vical portion of the cord, entering the inferior cervical ganglion, and thence 
passing to the heart ; (2) an inhibitory or retarding influence upon the 
action of the heart, through fibres of the spinal accessory nerve running in 
the trunk of the pneumogastric. 

8. A Vaso-motor centre, which by alternately contracting and dilating the 
blood vessels regulates the quantity of blood distributed to an organ or 

G 



90 HUMAN PHYSIOLOGY. 

tissue, and thus influences nutrition, secretion and calorification. The 
vaso-motor centre is situated in the medulla oblongata and pons Varolii, 
between the coipora quadrigemina and the calamus sci'iptorius. The 
vaso-motor fibres descend through the interior of the cord, emerge through 
the anterior roots of spinal nerves, enter the ganglia of the sympathetic, and 
thence pass to the walls of the blood vessels, and maintain the arterial 
tonus; they may be divided into two classes, viz: vaso-dilators, e.g., 
chorda tympani, and vaso-constrictors, e. g. sympathetic fibres. 

9. A diabetic centre, puncture of which causes an increase in the amount 
of urine secreted, and the appearance of a considerable quantity of sugar. 

10. A Respiratory centre, situated near the origin of the pneumogastric 
nerves, presides over the movements of respiration and its modifications, 
laughing, sighing, sobbing, sneezing, etc. It may be excited refiexly by 
the presence of carbonic acid in the lungs irritating the terminal pneumo- 
gastric filaments ; or automatically, according to the character of the blood 
circulating through it; an excess of carbonic acid, or a diminution . of 
oxygen, increasing the number of respiratory movements ; a reverse con- 
dition diminishing the respiratory movements. 

NERVOUS CIRCLE OF RESPIRATION (ENTIRELY REFLEX). 
Pulmonary branches of the pneumogastric. 
Lxcitor Superior laryngeal. 

Centripetal ] Trifacial > or 5th pair. ; 
Nerves Nerves of general sensibility. 

[ Sympathetic nerve. 

Phrenic, distributed to the diaphragm. 
Intercostals, distributed to the intercostal muscles, 

~ y. l r -, -I Facial nerve, or portio dura, to the facial muscles. 
Centrifugal j . r 

Nerves. External branch of spinal accessory, to the trape- 

[ zius and stemo-cleido-mastoid muscles. 

PONS VAROLII. 

The Pons Varolii unites together the cerebrum above, the cerebellum 
behind, and the medulla oblongata below. It consists of transverse and 
longitudinal fibres, amidst which are irregularly scattered collections of 
grey or vesicular nervous matter. 

The transverse fibres unite the two lateral halves of the cerebellum. 

The longitudinal fibres are continuous (i) with the anterior pyramids of 
the medulla oblongata, which, interlacing with the deep layers of the 
transverse fibres, ascend to the crura cerebri, forming their superficial or 
fasciculated portions. (2) With fibres derived from the olivary fasciculus, 



Motor 
or 



CORPORA QUADRIGEMINA. 91 

some of which pass to the tubercula quadrigemina, while others, uniting 
with fibres from the lateral and posterior columns of the medulla, ascend 
in the deep or posterior portions of the crura cerebri. 

Properties and Functions. The superficial portion is insensible and 
inexcitable to direct irritation ; the deeper portions appear to be excitable, 
consisting of descending motor fibres ; the posterior portions are sensible 
but inexcitable to irritation. 

Transmits motor impulses and sensory impressions from and to the 
cerebrum. 

The grey ganglionic matter consists of centres which convert impres- 
sions into conscious sensations, and originate motor impulses, these taking 
place independent of any intellectual process ; they are the seat of instinct- 
ive reflex acts ; the centres which coordinate the automatic movements of 
station and progression. 

CRURA CEREBRI. 

The Crura Cerebri are largely composed of the longitudinal fibres of 
the pons (anterior pyramids, fasciculi teretes) ; after emerging from the 
pons they increase in size, and become separated into two portions by a 
layer of dark grey matter, the locus niger. 

The superficial portion, composed of the anterior pyramids, constitutes 
the motor tract, which terminates/for the most part, in the corpus striatum, 
but to some extent, also, in the cerebrum ; the deep portion, made up of 
the fasciculi teretes and posterior pyramids and accessory fibres from the 
cerebellum, constitute the sensory tract (the tegmentum}, which terminates 
in the optic thalamus and cerebrum. 

Function. The crura are conductors of motor impulses and sensory 
impressions ; the grey matter, the locus niger, assists in the coordination 
of the complicated movements of the eyeball and iris, through the motor 
oculi communis nerve. They also assist in the harmonization of general 
muscular movements ; section of one crus giving rise to peculiar move- 
ments of rotation, and somersaults forward and backward. 

CORPORA QUADRIGEMINA. 

The Corpora Quadrigemina are four small, rounded eminences, two 
on each side of the median line, situated immediately behind the third 
ventricle, and beneath the posterior border of the corpus callosum. 

The anterior tubercles are oblong from before backwards, and larger 
than the posterior, which are hemispherical in shape ; they are greyish in 
color, but consist of white matter externally and gray matter internally. 



92 HUMAN PHYSIOLOGY. 

Both the anterior and posterior tubercles- are connected with the optic 
thalami by commissural bands named the anterior and posterior brachia, 
respectively. They receive fibres from the olivary fasciculus and fibres from 
the cerebellum, which pass upward to enter the optic thalami. 

The corpora geniculata are situated, one on the inner side and one on 
the outer side of each optic tract, behind and beneath the optic thalamus, 
and from their position are named the corpora geniculata interna and ex- 
terna ; they give origin to fibres of the optic nerve. 

Functions. The tuber cula quadrigemina are the physical centres of 
sight, translating the luminous impressions into visual sensations. Destruc- 
tion of these tubercles is immediately followed by a loss of the sense of 
sight ; moreover, their action in vision is crossed, owing to the decussation 
of the optic tracts, so that if the tubercle of the right side be destroyed by 
disease or extirpated, in a pigeon, the sight is lost in the eye of the oppo- 
site side, and the iris loses its mobility. 

The tubercula quadrigemina as nerve centres preside over the reflex 
movements which cause a dilation or contraction of the iris; irritation of 
the tubercles causing contraction, destruction causing dilatation. Removal 
of the tubercles on one side produces a temporary loss of power of the 
opposite side of the body, and a tendency to move around an axis is 
manifested, as after a section of one crus cerebri, which, however, may be 
due to giddiness and loss of sight. 

They also assist in the coordination of the complex movements of the 
eye, and regulate the movements of the iris during the movements of 
accommodation for distance. 

CORPORA STRIATA AND OPTIC THALAMI. 

The Corpora Striata are two large ovoid collections of grey matter, 
situated at the base of the cerebrum, the larger portions of which are im- 
bedded in the white matter, the smaller portions projecting into the ante- 
rior part of the lateral ventricle. Each striated body is divided by a 
narrow band of white matter, into two portions, viz : 

1. The caudate nucleus, the intraventricular portion, which is conical 
in shape, having its apex directed backwards, as a narrow, tail-like process. 

2. The lenticular nucleus, imbedded in the white matter, and for the 
most part external to the ventricle; on the outer side of the lenticular 
nucleus is found a narrow band of white matter, the external capsule ; 
and between it and the convolutions of the island of Reil, a thin band of 
grey matter, the claustrum; the corpora striata are greyish in color, and 



CEREBELLUM. 93 

when divided present transverse striations, from the intermingling of white 
fibre and grey cells. 

The Optic Thalami are two oblong masses situated in the ventricles 
posterior to the corpora striata, and resting upon the posterior portion of 
the crura cerebri. The internal surface projecting into the lateral ven- 
tricles, is white, but in their interior they are greyish, from a commingling 
of both white fibres and grey cells. Between the lenticular nucleus and 
the optic thalamus is a band of white tissue, the internal capsule, partly 
consisting of fibres passing up to the cerebrum from the crura. 

Functions. The corpora striata are the centres in which terminate 
most of the fibres of the superficial or motor tract of the crura cerebri ; 
others pass upward through the internal capsule, to be distributed to the 
cerebrum. It might be inferred, from their anatomical relation, that they 
are motor centres ; irritation by a weak galvanic current produces mus- 
cular movements of the opposite side of the body ; destruction of their 
substance by a hemorrhage, as in apoplexy, is followed by a paralysis of 
motion of the opposite side of the body, but there is no loss of sensation. 
Their precise function is unknown, but in some way connected with motion. 

The optic thalami receive the fibres of the teg7?ientum, the posterior 
portion of the crura cerebri. They are insensible and inexcitable to direct 
irritation. Removal of one optic thalamus, or destruction of its substance by 
disease or hemorrhage, is followed by a loss of sensibility of the opposite, 
but there is no loss of motion; their precise function is also unknown, but in 
some way connected with sensation. In both cases their action is crossed. 

CEREBELLUM. 

The Cerebellum is situated in the inferior fossae of the occipital bone, 
beneath the posterior lobes of the cerebrum. It attains its maximum 
weight, which is about 5 oz., between the twenty-fifth and fortieth years; 
the proportion between the cerebellum and cerebrum being I to Sf. 

It is composed of two lateral hemispheres and a central elongated lobe, 
the vermiform process ; the two ^hemispheres are connected with each 
other by the fibres of the middle peduncle forming the superficial portion 
of the pons Varolii. It is brought into connection with the medulla 
oblongata and spinal cord, through the prolongation of the restiform bodies ; 
with the cerebrum, by a fasciculus of fibres passing to the corpora quadri- 
gemina, beneath which they pass to the optic thalamus, and then form 
part of the diverging cerebral fibres. 

Structure. It is composed of both white and grey matter, the former 
being internal, the latter external, and convoluted, for economy of space. 



94 HUMAN PHYSIOLOGY. 

The white matter consists of a central stem, in the interior of which is 
a dentated capsule of grey matter, the corpus dent atum. From the external 
surface of the stem of white matter, processes are given off, forming the 
lamina* which are covered with grey matter. 

The grey matter is convoluted and covers externally, the laminated pro- 
cesses; a vertical section through the grey matter reveals the following 
structures : — 

1 . A delicate connective tissue layer, just beneath the pia mater, contain- 
ing rounded corpuscles, and branching fibres passing toward the external 
surface. 

2. The cells of Purkinje, forming a layer of large, nucleated, branched 
nerve cells sending off processes to the external layer. 

3. A granular layer of small, but numerous corpuscles. 

4. Nerve fibre layer, formed by a portion of the white matter. 

Properties and Functions. Irritation of the cerebellum is not fol- 
lowed by any evidences either of pain or convulsive movements; it is, 
therefore, insensible and inexcitable. 

Co-ordination of Movements. Removal of the superficial portions 
of the cerebellum in pigeons produces feebleness and want of harmony 
in the muscular movements; as successive slices are removed, the move- 
ments become more irregular, and the pigeon becomes restless; when 
the last portions are removed, all power of flying, walking, standing, etc., 
is entirely gone, and the equilibrium cannot be maintained ; the power of 
coordinating muscular movements being entirely gone. The same results 
have been obtained by operating on all. classes of animals. 

The following symptoms were noticed by Wagner, after removing the 
whole or a large part of the cerebellum. 1. A tendency on the part of 
the animal to throw itself on one side, and to extend the legs as far as 
possible. 2. Torsion of the head on the neck. 3. Trembling of the 
muscles of the body, which was general. 4. Vomiting and occasionally 
liquid evacuations. 

Forced Movements. Division of one crura cerebelli causes the animal 
to fall on one side and roll rapidly on its longitudinal axis. According to 
Schiff, if the peduncle be divided from behi7id, the animal falls on the 
same side as the injury ; if the section be made in front the animal turns 
to the opposite side. 

Disease of the cerebellum partially corroborates the results of experi- 
ments ; in many cases symptoms of unsteadiness of gait, from a want of 
coordination have been noticed. 

Comparative anatomy reveals a remarkable correspondence between 



CEREBRUM. 95 

the development of the cerebellum and the complexity of muscular actions. 
It attains a much greater development, relatively to the rest of the brain, 
in those animals whose movements are very complex and varied in char- 
acter, such as the kangaroo, shark and swallow. 

The cerebellum may possibly exert some influence over the sexual func- 
tion, but physiological and pathological facts are opposed to the idea of 
its being the seat of the sexual iustinct. It appears to be simply a centre 
for the coordination and equilibration of muscular movements. 

CEREBRUM. 

The Cerebrum is the largest portion of the encephalic mass, constitu- 
ting about four-fifths of its weight ; the average weight in the adult male 
is from 48 to 50 oz., or about 3 pounds, while in the adult female it is 
about 5 oz. less. After the age of 40 the weight of the cerebrum gradually 
diminishes at the rate of one ounce every ten years. In the brain of 
idiots the amount is often lower than normal, and at times weighing not 
more than 20 ounces. 

The Blood Supply to the cerebrum is unusually large, considering its 
comparative bulk ; nearly one-fifth of the entire volume of blood being 
distributed to it by the carotid and vertebral arteries. These vessels anas- 
tomose so freely, and are so arranged within the cavity of the cranium, that 
an obstruction in one vessel will not interfere with the regular supply of 
blood to the parts to which its branches are distributed. A diminished 
amount, or complete cessation, of the supply of blood is at once followed 
by a suspension of its functional activity. 

The cerebrum is connected with the pons Varolii and medulla oblongata 
through the crura cerebri, and with the cerebellum, through its superior 
peduncles. It is divided into two lateral halves, or hemispheres, by the 
longitudinal fissure running from before backwards in the median line ; 
each hemisphere is composed of both white and grey matter, the former 
being internal, the latter external ; it covers the surfaces of the hemispheres 
which are infolded, forming convolutions, for economy of space. 

Fissures. 

1. The. fissure of Sylvius is one of the most important; it is the first to 
appear in the development of the foetal brain, being visible at about the 
third month; in the adult it is quite deep and well marked, running from 
the under surface of the brain upward, outward, and backward, and 
forms a boundary between the frontal and temporo-sphenoidal lobes. 

2. The fissure of Rolando is second in importance, and runs from a 



96 HUMAN PHYSIOLOGY. 

point on the convexity near the median line transversely outward and 
downward towards the fissure of Sylvius, but does not enter it. It sepa- 
rates the frontal from the parietal lobe. 

3. The parietal fissure, arising a short distance behind the fissure of 
Rolando, upon the convexity of the hemisphere, runs downward and 
backward to its posterior extremity. 

Secondary fissures of importance are found in different lobes of the 
cerebrum, separating the various convolutions. In the anterior lobe are 
found the pre-central, superior frontal and inferior frontal fissures ; in the 
occipital lobe, are found the parietooccipital and the calcarine fissures. 

Convolutions. Frontal Lobe. 

The Ascending frontal convolution, situated in front of the fissure of 
Rolando, runs downward and forward; it is continuous above with the 
anterior frontal, and below with the inferior frontal convolution. 

The Superior frontal convolution is bounded internally by the longitu- 
dinal fissure, and externally by the superior frontal fissure; it is connected 
with the superior end of the frontal convolution, and runs downward and 
forward to the anterior extremity of the frontal lobe, where it turns back- 
ward, and rests upon the orbital plate of the frontal bone. 

The Middle frontal convolution, the largest of the three, runs from be- 
hind forward, along the sides of the lobe, to its anterior part ; it is bounded 
above by the superior and below by the inferior frontal fissures. 

The Inferior frontal convolution winds around the ascending branch of 
the fissure of Sylvius, in the anterior and inferior portion of the cerebrum. 

Parietal L be. The Ascending parietal convolution is situated just be- 
hind the fissure of Rolando, running downward and forward ; above, it 
becomes continuous with the upper parietal convolution, and below, winds 
around to be united with the ascending frontal. 

The Upper parietal convolution is situated between the parietal and 
longitudinal fissures. 

The Supra- marginal convolution winds around the superior extremity 
of the fissure of Sylvius. 

The Angular convolution, a continuation of the preceding, follows the 
parietal fissure to its posterior extremity, and then makes a sharp angle 
downward and forward. 

Tempore- Sphenoidal Lobe. Contains three well marked convolutions, 
the superior, middle and inferior, separated by well defined fissures, and 
continuous posteriorly with the convolutions of the parietal lobe. 

The Occipital Lobe lies behind the parietooccipital fissure, and contains 
the superior, middle and inferior convolutions, not well marked. 



CEREBRUM. 97 

The Central Lobe or Island of Reil y situated at the bifurcation of the 
fissure of Sylvius, is a triangular-shaped cluster of six convolutions, the 
gyri operti, which are connected with those of the frontal, parietal, and 
temporo- sphenoidal lobes. 

Structure. The Grey ?natter of the cerebrum, about one-eighth of an 
inch thick, is composed of five layers of nerve cells: (i) a superficial layer, 
containing few small multipolar ganglion cells; (2) small ganglion cells, 
pyramidal in shape ; (3) a layer of large pyramidal ganglion cells with 
processes running off superiorly and laterally ; (4) the granular formation 
containing nerve cells; (5) spindle-shaped and branching nerve cells of 
moderate size. 

The White Matter consists of three distinct sets of fibres — 

1. The diverging or peduncular fibres are mainly derived from the 
columns of the cord and medulla oblongata ; passing upward through the 
crura cerebri, they receive accessory fibres from the olivary fasciculus, 
corpora quadrigemina and cerebellum. Some of the fibres terminate in 
the optic thalami and corpora striata, while others radiate into the anterior, 
middle and posterior lobes of the cerebrum. 

2. The transverse commissural fibres connect together the two hemi- 
spheres, through the corpus callosum and anterior and posterior commis- 
sures. 

3. The longitudinal commissural fibres connect together different parts 
of the same hemisphere. 

Functions. The cerebral hemispheres are the centres of the nervous 
system through which are manifested all the phenomena of the mind ; 
they are the centres in which impressions are registered, and reproduced 
subsequently as ideas; they are the seat of intelligence, reason, and will. 

However important a centre the cerebrum may be, for the exhibition of 
this highest form of nervous action, it is not directly essential for the con- 
tinuance of life ; for it does not exert any control over those automatic 
reflex acts, such as respiration, circulation, etc., which regulate the func- 
tions of organic life. 

From a study of comparative anatomy, pathology, vivisection, etc., evi- 
dence has been obtained which throws some light upon the physiology of 
the cerebral hemispheres. 

I. Comparative Anatomy shows that there is a general connection be- 
tween the size of the brain, its texture, the depth and number of its convo- 
lutions, and the exhibition of mental, power. Throughout the entire ani- 
mal series, the increase of intelligence goes hand in hand with an increase 
in the development of the br^in. In man there is an enormous increase 



98 HUMAN PHYSIOLOGY. 

in size over that of the highest animals, the anthropoids. The most culti- 
vated races of men have the greatest cranial capacity ; that of the educated 
European being about 116 cubic inches, that of the Australian being about 
60 cubic inches, a difference of 56 cubic inches. Men distinguished for 
great mental power usually have large and well developed brains ; that of 
Cuvier weighed 64 oz. ; that of Abercrombie 63 oz. ; the average being about 
48 to 50 oz. ; not only the size, but above all, the texture of the brain, 
must be taken into consideration. 

2. Pathology. Any severe injury or disease disorganizing the hemi- 
spheres is at once attended by a disturbance, or entire suspension of mental 
activity. A blow on the head producing concussion, or undue pressure 
from cerebral hemorrhage, destroys consciousness ; physical and chemical 
alterations in the grey matter have been shown to coexist with insanity, 
loss of memory, speech, etc. Congenital defects of organization from im- 
perfect development are usually accompanied by a corresponding deficiency 
of intellectual power and the higher instincts. Under these circumstances 
no great advance in mental development can be possible, and the intelli- 
gence remains at a low grade. In congenital idiocy not only is the brain 
of small size, but it is wanting in proper chemical composition ; phosphorus , 
a characteristic ingredient of the nervous tissue, being largely diminished in 
amount. 

3. Experimentation upon the lower animals by removing the cerebral 
hemispheres is attended by results similar to those observed in disease and 
injury. Removal of the cerebrum in pigeons produces complete abolition 
of intelligence, and destroys the capability of performing spontaneous 
movements. The pigeon remains in a condition of profound stupor, which 
is not accompanied, however, by a loss of sensation, or the power of pro- 
ducing reflex or instinctive movements. The pigeon can be temporarily 
aroused by pinching the feet, loud noises, light placed before the eyes, etc., 
but soon relapses into a state of quietude, being unable to remember im- 
pressions and connect them with any train of ideas ; the faculties of 
memory, reason and judgment being completely abolished. 

LOCALIZATION OF FUNCTIONS. 

The Fatuity of articulate language, by which the individual associates 
ideas and words, comprises two distinct faculties, viz : — 1. The power of 
recalling particular words; 2. The coordination of muscles necessary for 
their articulation. 

Aphasia is a condition in which the power of expressing ideas in words 
is completely lost. Pathological observation has shown that this condition 



.CEREBRUM. 99 

is frequently associated with disease of the jd frontal convolution of the 
left side, and also the convolutions of the island of Reil, parts nourished by 
the middle cerebral artery. It usually coexists with right hemiplegia; at 
times aphasia results from disease of corresponding structures of the right 
side. The faculty of articulate language may be located in the 3d frontal 
convolution and the island of Reil, usually on the left side of the brain. 

Motor Centres. The grey matter covering the cerebral hemispheres 
is both insensible and inexcitable to ordinary mechanical and chemical 
stimuli ; but when a galvanic current of low intensity is applied to par- 
ticular regions of the cerebrum of a monkey, in which the general ar- 
rangement of the convolutions approximates that of man, definite coordi- 
nate movements occur on the opposite side of the body, e. g., rotation, 
flexion and extension of the limbs, and movements of the facial muscles. 

The regions in which the motor centres are located are the convolutions 
around the fissure of Rolando, especially the ascending frontal and the 
ascending parietal. Destruction of the grey matter of these convolutions 
is followed by a paralysis of motion on the opposite side of the body; 
destruction of circumscribed areas in these convolutions causes paralysis 
of the groups of muscles excited to action by electrical stimulation of such 
areas. 

The antero-frontal and occipital lobes are not excitable to electrical 
stimulation. 

Special Centres. The superior and 7?iiddle frontal convolutions appear 
to be connected with the intellectual faculties ; ablation of these convolu- 
tions causes a marked impairment of the intelligence and of the faculty of 
attentive observation, without impairing either sensation or motion. 

The Visual centre is located in the angular convolution. If this centre 
be destroyed, blindness of the opposite eye results, which is, however, only 
temporary if the opposite angular convolution be intact ; destruction of 
both causts a complete and permanent loss of visual perceptions. 

The Auditory and Taste centres are located in the superior and inferior 
temporo-sphenoidal convolutions respectively; destruction of these regions 
abolishes the sense of hearing and taste. The sense of s?nell is situated in 
the uncinate convolution or cornu ammonis. 

Systemic sensations are probably located in the occipital lobes ; their 
ablation is followed by a state of great depression, loss of appetite, and a 
refusal to take food. 

The centre for sensory impressions is located in the posterior portion of 
the cerebrum ; destruction of the posterior portion of the internal capsule 
causes loss of sensation on the opposite side of body. 



100 HUMAN PHYSIOLOGY. 

SYMPATHETIC NERVOUS SYSTEM. 

The Sympathetic Nervous System consists of a chain of ganglia 
connected together hy longitudinal nerve filaments, situated on each side 
of the spinal column, running from above downward. The two gangli- 
onic cords are connected together in the interior of the cranium by the 
ganglion of Ribes, on the anterior communicating artery, and terminate in 
the ganglion impar, situated at the tip of the coccyx, 

The chain of ganglia is divided into groups and named according to the 
localities in which they are found, viz • Cranial, four in number ; cervi- 
cal, three; thoracic, twelve; lumbar, five; sacral, five; coccygeal, one. 
Each ganglion consists of a collection of vesicular nervous matter, among 
which are found tubular and gelatinous nerve fibres. The ganglia are 
reinforced by motor and sensory fibres from the cerebro-spinal nervous 
system. 

The Ganglia are distinct nerve centres, from which branches are dis- 
tributed to glands, arteries, muscles, and to the cerebral and spinal nerves ; 
many pass, also, to the visceral ganglia, e.g., cardiac, semilunar, pelvic, etc. 

Cephalic Ganglia. 

1. The Ophthalmic or Ciliary ganglion is situated in the orbital cavity 
posterior to the eyeball; it is of small size, and of a reddish grey color; 
receives filaments of communication from the motor oculi, ophthalmic 
branch of the 5th pair, and the carotid plexus. Its filaments of distribu- 
tion are the ciliary nerves which pass to the iris and ciliary muscle. 

Function. It is the centre through which the reflex acts take place by 
which the pupilis contracted or dilated; controls the movement of ac- 
commodation for vision at different distances. 

2. The Spheno-palatine, or Meckel's ganglion, triangular in shape, is 
situated in the spheno-maxillary fossa ; receives filaments from the facial 
(Vidian nerve), and the superior maxillary branch of the 5th nerve. Its 
filaments of distribution pass to the gums, the soft palate, levator paiati, 
and azygos uvulae muscles. 

3. The Otic, or Arnold's ganglion, is of small size, oval in shape, and 
situated beneath the foramen ovale ; receives a motor filament from the 
facial and sensory filaments from -the glossopharyngeal and 5th nerve; 
sends filaments to the mucous membrane of the tympanic cavity and to 
the tensor tympani muscle. 

4. The Sub-maxillary ganglion, situated in the sub-maxillary gland, 
receives motor filaments from the chorda tympani and sensory filaments 



SYMPATHETIC NERVOUS SYSTEM. 101 

from the lingual branch of the 5th nerve. Regulates to some extent the 
secretion of saliva. 

Cervical Ganglia. 

The Superior cervical ganglion is fusiform in shape, of a greyish-red 
color, and situated opposite the 2d and 3d cervical vertebra; it sends 
branches to form the carotid and cavernous plexuses which follow the 
course of the carotid arteries to their distribution; also sends branches 
to join the glossopharyngeal and pneumogastric to form the pharyngeal 
plexus. 

The Middle cervical ganglion, the smallest of the three, is occasionally 
wanting ; it is situated opposite the 5th cervical vertebra ; sends branches 
to the superior and inferior cervical ganglion, and to the thyroid artery. 

The Inferior cervical ganglion, irregular in form, is situated opposite the 
last cervical. vertebra ; it is frequently fused with the first thoracic ganglion. 

The superior, middle and inferior cardiac nerves, arising from these 
cervical ganglia, pass downward and forward to form the deep and super- 
ficial cardiac plexuses located at the bifurcation of the trachea, from which 
branches are distributed to the heart, coronary arteries, etc. 

The Thoracic Ganglia are usually twelve in number, placed against 
the heads of the ribs behind the pleura ; they are small in size and grey in 
color; they communicate with the cerebro-spinal nerves by two filaments, 
one of which is white, the other grey. 

The great splanchnic nerve is formed by the union of branches from the 
sixth, seventh, eighth and ninth ganglia ; it passes through the diaphragm 
to the semi-lunar ganglion. 

The lesser splanchnic nerve is formed by the union of filaments from the 
tenth and eleventh ganglia, and is distributed to the coeliac plexus. 

The renal splanchnic nerve arises from the last thoracic ganglion and 
terminates in the renal plexus. 

The semi-lunar ganglia, the largest of the sympathetic, are situated by 
the side of the coeliac axis ; they send radiating branches to form the solar 
plexus ; from the various plexuses, nerves follow the gastric, splenic, 
hepatic, renal, etc., arteries, into the different abdominal viscera. 

The Lumbar Ganglia, four in number, are placed upon the bodies of 
the vertebra ; they give off branches which unite to form the aortic, lumbar 
plexus and the hypogastric plexus, and follow the blood vessels to their 
terminations. 

The Sacral and Coccygeal Ganglia send filaments of distribution 
to all the blood vessels of the pelvic viscera. 



102 HUMAN PHYSIOLOGY. 

Properties and Functions. The sympathetic nerve possesses both 
sensibility and the power of exciting motion, but these properties are much 
less decided than in the cerebro-spinal system. Irritation of the ganglia 
does not produce any evidence of pain until some time has elapsed. If 
caustic soda be applied to the semi-lunar ganglia, or a galvanic current be 
passed through the splanchnic nerves, no instantaneous effect is noticed, as 
in the case of the cerebro-spinal nerves ; but in the course of a few seconds 
a slow, progressive contraction of the muscular coat of the intestines is 
established, which continues for some time after the irritation is removed. 
Division of the sympathetic nerve in the neck is followed by a vascular 
congestion of the parts above the section on the corresponding side, attended 
by an increase in the temperature ; not only is there an increase in the 
amount of blood, but the rapidity of the blood current is very much 
hastened, and the blood in the veins becomes of a brighter color. Gal- 
vanization of the upper end of the divided nerve causes all of the preceding 
phenomena to disappear ; the congestion decreases, the temperature falls, 
and the venous blood becomes dark again. 

The sympathetic exerts a similar influence upon the circulation of the 
limbs and the glandular organs ; destruction of the first thoracic ganglion 
and division of the lumbar nerves is followed by a dilatation of the vessels, 
an increased rapidity of the circulation, and an elevation of temperature in 
the anterior and posterior limbs; galvanization of the peripheral ends 
causes all of these phenomena to disappear. The same is true for the 
glandular organs. 

The Vaso-motor Nerves, which are contained in the branches of the 
sympathetic system, and which regulate the calibre of the blood vessels, 
do not arise in the sympathetic ganglia, but are derived exclusively from 
the cerebro-spinal system. 

Sleep is a periodical condition of the nervous system, in which there is 
a partial or complete cessation of the activities of the higher nerve centres. 
The cause of sleep is a diminution in the quantity of blood, occasioned by 
a contraction of the smaller arteries under the influence of the vaso-motor 
nerves. 

During the waking state, the brain undergoes a physiological waste as a 
result of the exercise of its functions ; after a certain length of time its 
activities become enfeebled, and a condition of repose ensues, during which 
a regeneration of its substance takes place. 

When the brain becomes enfeebled there is a diminished molecular 
activity and an accumulation of waste products ; under these circumstances 



THE SENSE OF TOUCH. 103 

it ceases to dominate the medulla oblongata and the spinal cord. These 
centres then act more vigorously, and diminish the calibre of the cerebral 
blood vessels through the action of the vaso-motor nerves, producing a con- 
dition of physiological anaemia and sleep ; during this state waste products 
are removed, force is stored up, nutrition is restored, and waking finally 
occurs. 

THE SENSE OF TOUCH. 

The Sense of Touch is a modification of general sensibility, and 
located in the skin, which is especially adapted for this purpose, on account 
of the number of nerves and papillary elevations it possesses. The struc- 
tures of the skin and the modes of terminations of the sensory nerves has 
already been considered (see pages 60, 66). 

The Tactile Sensibility varies in acuteness in different portions of 
the body ; being most marked in those regions in which the tactile corpus- 
cles are most abundant, e. g., the palmar surfaces of the third phalanges 
of the fingers and thumb. 

The relative sensibility of different portions of the body has been ascer- 
tained by means of a pair of compasses, the points of which are guarded 
by cork, and then determining how closely they could be brought together, 
and yet be felt at two distinct points. The following are some of the 
measurements : — 

Point of tongue y^ of aline. 

Palmar surface of third phalanx I line. 

Red surface of lips 2 lines. 

Palmar surface of metacarpus 3 

Tip of the nose 3 

Part of lips covered by skin 4 

Palm of hand 5 

Lower part of forehead 10 

Back of hand 14 

Dorsum of foot 18 

Middle of the thigh 30 

The sense of touch communicates to the mind the idea of resistance 
only, and the varying degrees of resistance offered to the sensory nerves 
enables us to estimate, with the aid of the muscular sense, the qualities of 
hardness and softness of external objects. The idea of space or exten- 
sion is obtained when the sensory surface or the external object changes 
its place in regard to the other ; the character of the surface, its rough- 
ness or smoothness, is estimated by the impressions made upon the tactile 
papillae. 



104 HUMAN PHYSIOLOGY. 

Appreciation of Temperature. The general surface of the body is more 
or less sensitive to differences of temperature, though this sensation is 
separate from that of touch ; whether there are nerves especially adapted 
for the conduction of this sensation has not been fully determined. Under 
pathological conditions, however, the sense of touch may be abolished, 
while the appreciation of changes in temperature may. remain normal. 

The cutaneous surface varies in its sensibility to temperature in different 
parts of the body, and depends, to some extent, upon the thickness of the 
skin, exposure, habit, etc.; the inner surface of the elbow is more sensi- 
tive to changes in temperature than the outer portion of the arm ; the left 
hand is more sensitive than the right ; the mucous membrane less so than 
the skin. 

Excessive heat or cold has the same effect upon the sensibility ; the 
temperatures most readily appreciated are those between 50 F., and 1 15 F. 

The. sensations of pain and tickling appear to be conducted to the 
brain, also, by nerves different from those of touch ; in abnormal con- 
ditions the appreciation of pain may be entirely lost, while touch remains 
unimpaired. 

THE SENSE OF TASTE. 

The Sense of Taste is localized mainly in the mucous membrane 
covering the superior surface of the tongue. 

The Tongue is situated in the floor of the mouth ; its base is directed 
backward, and connected with the hyoid bone, by numerous muscles, with 
the epiglottis and soft palate ; its apex is directed forward against the pos- 
terior surface of the teeth. 

The substance of the tongue is made up of intrinsic muscular fibres, 
the linguales ; it is attached to surrounding parts, and its various move- 
ments performed by the extrinsic muscles, e. g., stylo-glossus, genio-hyo- 
glossus, etc. 

The mucous membrane covering the tongue is continuous with that 
lining the commencement of the alimentary canal, and is furnished with 
vascular and nervous papillae. 

The pap HIce are analogous in their structure to those of the skin, and 
are distributed over the dorsum of the tongue, giving to it its character- 
istic roughness. 

There are three principal varieties: — 

1. The filiform papilla are most numerous, and cover the anterior two- 
thirds of the tongue ; they are conical or filiform in shape, often pro- 
longed into filamentous tufts, of a whitish color, and covered by horny 
epithelium. 



THE SENSE OF TASTE. 105 

2. The fungiform papilla are found chiefly at the tip and sides of the 
tongue ; they are larger than the preceding, and may be recognized by 
their deep red color. 

3. The circumv allate papillcs are rounded eminences, from 8 to 10 in 
number, situated at the base of the tongue, where they form a V-shaped 
figure. They are quite large, and consist of a central projection of mu- 
cous membrane, surrounded by a wall, or circumvallation, from which 
they derive their name. 

The Taste Beakers, supposed to be the true organs of taste, are flask- 
like bodies, ovoid in form, about the -g-^th of an inch in length, situated 
in the epithelial covering of the mucous membrane, on the circumvallate 
papillae. They consist of a number of fusiform, narrow cells, and curved so 
as to form the walls of this flask-like body ; in the interior are elongated • 
cells, with large, clear nuclei, the taste cells. 

Nerves of Taste. The chorda tympani nerve, a branch of the facial, 
after leaving the cavity of the tympanum, joins the 3d division of the 5th 
nerve between the two pterygoid muscles, and then passes forward in the 
lingual branches, to be distributed to the mucous membrane of the anterior 
two-thirds of the tongue. Division or disease of this nerve is followed 
by a loss of taste in the part to which it is distributed. 

The glossopharyngeal enters the tongue at the posterior border of the 
hyo-glossus muscle, and is distributed to the mucous membrane of the base 
and sides of the tongue, fauces, etc. 

The trifacial nerve endows the tongue with general sensibility; the 
hypoglossal endows it with motion. 

The nerves of taste in the superficial layer of the mucous membrane 
form a fine plexus from which branches pass to the epithelium and pene- 
trate it ; others enter the taste beakers, and are directly connected with 
the taste cells. 

The seat of the sense of taste has been shown by experiment to be the 
whole of the mucous membrane over the dorsum of the tongue, soft pal- 
ate, fauces, and upper part of the pharynx. 

The Sense of Taste enables us to distinguish the savor of substances 
introduced into the mouth, which is different from tactile sensibility. The 
sapid qualities of substances appreciated by the tongue are designated as 
bitter, sweet, alkaline, sour, salt, etc. 

The Essential Conditions for the production of the impressions of 
taste are (1) a state of solubility of the food; (2) a free secretion of the 
saliva, and (3) active movements on the part of the tongue, exerting 
H 



106 HUMAN PHYSIOLOGY. 

pressure against the roof of the mouth, gums, etc., thus aiding the solution 
of various articles and their osmosis into the lingual papillae. Sapid sub- 
stances, when in a state of solution, pass into the interior of trie taste 
beakers and come into contact, through the medium of the taste cells, 
with the terminal filaments of the gustatory nerves. 

THE SENSE OF SMELL. 

The Sense of Smell is located in the mucous membrane lining the 
upper part of the nasal cavity, in which the olfactory nerves are distributed. 

The Nasal Fossas are two cavities, irregular in shape, separated by 
the vomer, the perpendicular plate of the ethmoid bone, and the triangular 
cartilage. They open anteriorly and posteriorly by the anterior and pos- 
terior nares, the latter communicating with the pharynx. They are lined 
by mucous membrane, of which the only portion capable of receiving 
odorous impressions is the part lining the upper one -third of the fossae. 

The Olfactory Nerves, arising by three roots from the posterior and 
inferior surface of the anterior lobes, pass forward to the cribriform plate of 
the ethmoid bone, where they each expand into an oblong body, the olfactory 
bulb. From its under surface from 15 to 20 filaments pass downward 
through the foramina, to be distributed to the olfactory mucous membrane, 
where they terminate in long, delicate, spindle-shaped cells, the olfactory- 
cells, situated between the ordinary epithelial cells. 

The olfactory bulbs are the centres in which odorous impressions are 
perceived as sensations; destruction of these bulbs being attended by an 
abolition of the sense of smell. 

In animals which possess an acute sense of smell, there is a correspond- 
ing increase in the development of the olfactory bulbs. 

The Essential Conditions for the sense of smell are, (1) a special 
nerve centre capable of receiving impressions and transforming them into 
odorous sensations. (2) Emanations from bodies which are in a gaseous 
or vaporous condition. (3) The odorous emanations must be drawn 
freely through the nasal fossae ; if the odor be very faint, a peculiar inspiratory 
movement is made, by which the air is forcibly brought into contact with 
the olfactory filaments. The secretions of the nasal fossae probably dis- 
solve the odorous particles. 

Various substances, as ammonia, horseradish, etc., excite the sensi- 
bility of the mucous membrane, which must be distinguished from the per- 
ception of true odors. 



THE SENSE OF SIGHT. 107 

THE SENSE OF SIGHT. 

The Eyeball. The eyeball, or organ of vision, is situated within the 
orbital cavity, and loosely held in position by the fibrous capsule of Tenon. 
It rests upon a cushion of fat, which never disappears, except in cases of 
extreme starvation ; it is protected from injury by the bony orbital walls, 
and is so situated as to permit an extensive range of vision. 

Blood vessels and Nerves. The structures of the eyeball are sup- 
plied with blood by the ciliary arteries, which pierce the posterior surface 
around the optic nerve. 

The Ciliary or Ophthalmic ganglion, about the size of a pin's head, 
situated in the posterior portion of the orbital cavity, receives filaments of 
communication from the trifacial or 5th nerve, the motor-oculi or 3d nerve, 
and the sympathetic. From its anterior portion are given off the ciliary 
nerves, which enter the ball posteriorly and are distributed to the structures 
of which it is composed. 

Structure. The form of the eyeball is that of a sphere ; it is about 
one inch in the transverse diameter, and a little longer in the antero- 
posterior diameter, on account of its having the segment of a smaller sphere 
inserted into the anterior surface. It is composed of 3 coats ; in its inte- 
rior is contained the refracting apparatus. 

The Sclerotic and Cornea together form the external coat of the eye; 
the former covering the posterior -|th, the latter covering the anterior -J-th. 
The sclerotic is a dense, opaque, fibrous membrane, varying in thickness from 
the J^th to the ^th of an inch; it is composed of connective tissue and is 
slightly vascular. Posteriorly it is continuous with the sheath of the optic 
nerve, and is pierced by that nerve, as well as by the ciliary vessels and 
nerves ; anteriorly its fibres become quite pale, and after passing into the 
cornea, transparent. It is a protective covering, and gives attachment to 
the tendons of the muscles by which the eyeball is moved. 

The Cornea is a non-vascular, transparent membrane, composed for the 
most part of connective tissue in which are contained stellate corpuscles filled 
with a clear fluid. It is covered anteriorly by the basement membrane of 
the conjunctiva, upon which rests several layers of epithelial cells ; poste- 
riorly it is lined by the membrane of Descemet, which is reflected on to 
the anterior surface of the iris. 

The Choroid, the Iris, the Ciliary Muscle, and Ciliary Processes, 
together constitute the middle coat of the eye. 

The Choroid coat, about the -g^th of an inch in thickness, is both a vas- 
cular and pigmentary membrane ; it is of a dark brown color externally, 
and of a deep black internally. 



108 HUMAN PHYSIOLOGY, 

The outer portion is made up of a rich network of vessels, the branches 
of the ciliary arteries and veins ; the inner portion, the pigmentary layer, 
is a delicate membrane lined by hexagonal cells, containing black pigment. 

The function of the choroid is mainly to absorb the rays of light which 
pass through the retina, and thus prevent them from interfering with the 
distinctness of vision by being again reflected upon the retina. 

The Iris is a circular, muscular diaphragm, placed in the anterior por- 
tion of the eye, and perforated a little to the nasal side of the centre by a 
circular opening, the pupil ; it is attached by its periphery to the point of 
junction of the sclerotic and cornea. It is composed of a connective tissue 
stroma, blood vessels and non-striated muscular fibres, circular and radiat- 
ing. The circular fibres surround the margin of the pupil like a sphincter, 
and are controlled by the 3d pair of nerves ; the radiating fibres (dilators 
of the pupil) radiate from centre toward its circumference, and are con- 
trolled by the sympathetic system of nerves. 

The Ciliary muscle is a greyish circular band, consisting of unstriped 
muscular fibres, about one-eighth of an inch long, running from before 
backwards'; beneath the radiating fibres are small bands of circular fibres 
running around the eye. It arises from the line of junction of the sclerotic, 
cornea and iris ; passing backwards it is attached to the outer surface of 
the choroid ; it is the principal agent in accommodation, and innervated by 
the 3d pair of nerves. 

The Retina forms the internal coat of the eye ; in the fresh state it is a 
delicate, transparent membrane, but soon becomes opaque and of a pinkish 
tint ; it extends forward almost to the ciliary processes, where it terminates 
in the ora serrata. In the posterior portion of the retina, at a point cor- 
responding to the axis of vision, is a rounded, elevated, yellow spot, the 
limbus luteus, having a central depression, the fovea centralis ; about 
y^th of an inch to the inner side is the point of entrance'of the optic nerve, 
where it spreads out to assist in the formation of the retina. The artei'ia 
centralis retina pierces the optic nerve near the sclerotic, runs forward in its 
substance and is distributed in the retina as far forward as the ciliary processes. 

The Retina consists of nine distinct layers, from within outwards, sup- 
ported by connective tissue. I. Membrana limitans interna. 2. Fibres 
of optic nerve. 3. Layers of ganglionic corpuscles. 4. Molecular layer. 
5. Internal granular layer. 6. Molecular layer. 7. External granular 
layer. 8. Membrana limitans externa. 9. Layer of rods and cones. 

In the Fovea centralis, at the point of most distinct vision, all of the layers 
disappear except the layer of rods and cones, which become somewhat 
longer and more slender. 



THE SENSE OF SIGHT. 109 

The Aqueous humor is a clear fluid, alkaline in reaction, occupying the 
anterior chamber of the eye ; this chamber is bounded in front by the 
cornea, posteriorly by the iris. 

The Vitreous humor forms about four-fifths of the entire ball. It supports 
the retina, and is excavated anteriorly for the reception of the lens ; it is 
transparent, of a jelly-like consistence, and surrounded by a structureless, 
transparent membrane, the hyaloid membrane. 

The Crystalline lens is situated immediately behind the pupil, in the 
concavity of the vitreous humor. It is inclosed in a highly elastic, trans- 
parent membrane, the capsule. The lens is a transparent, doubly-convex 
body, i/j of an inch transversely, % of an inch antero-posteriorly ; it is 
held in position by the suspensory ligament, formed by a splitting of the 
hyaloid tunic, the external layer of which passes in front of the lens, the 
internal layer behind it. 

Vision. The eye may be regarded as a camera obscura, in which 
images of external objects are thrown upon a screen, the retina, by means 
of a double convex lens. 

The Essential Conditions for proper vision are : I. Certain refract- 
ing media, e. g., cornea, aqueous humor, and crystalline lens, by which 
the rays of light are so disposed as to form an image. 2. A diaphragm, 
the iris, which, by alternately contracting and dilating, increases or dimin- 
ishes the amount of light entering the eye. 3. A sensitive surface, to 
receive the image and transmit the luminous impressions through the optic 
nerve to the brain. 4. A contractile structure, the ciliary muscle, which 
can so manipulate the lens as to enable external objects to be seen at near 
or far distances. 

The Refracting Apparatus, by which parallel rays of light are 
brought to a focus on the retina, consists mainly of the crystalline lens, 
though aided by the cornea and aqueous humor. A ray of light passing 
through the pupil is refracted and concentrated by the lens at a given point 
posterior to it. For the correct perception of images of external objects, 
the rays of light must be accurately focused on the retina ; in order that 
this may be accomplished, the lens must have a certain density and a 
proper curvature of its surfaces. When the lens is too convex, its refract- 
ing power is greatly increased, the rays of light are brought to a focus in 
front of the retina, and the visual perception becomes dim and confused. 
When it is too flat, the rays are not focused at all, and the resulting per- 
ception is the same. 

The Crystalline lens, therefore, produces a distinct perception of the 
outline and form of external objects. 



110 HUMAN PHYSIOLOGY. 

Action of the Iris. The iris, consisting of contracting and dilating 
fibres, transmits and regulates the quantity of light passing throUghjts cen- 
tral aperture, the pupil, which is necessary for distinct vision. 

If the light be too intense or excessive, the circular fibres contract under 
the stimulus of the 3d pair of nerves, and the aperture is diminished in 
size; if the quantity of light be insufficient, the dilating fibres contract 
under the stimulus of the sympathetic, and the pupillary aperture is increased 
in size. 

The Retina, which is formed partly by the expansion of the optic 
nerve, and partly by new nervous structures, is the membrane which re- 
ceives the impressions of light. Its posterior surface, which is in contact 
with the choroid, and especially the layer of rods and cones, is the sensi- 
tive portion, in which the rays of light produce their effects. 

The paint of most distinct vision is in the macula lutea, and especially 
in its central depression, the fovea, which corresponds to the central axis 
of the eye ; it is situated about T ^-th of an inch to the outside of the entrance 
of the optic nerve. It is at this point that images of external objects are 
seen most distinctly, while all around it the perceptions are more or less 
obscure ; at the macula all the layers disappear except the layer of rods and 
cones. 

Blind Spot. At the point of entrance of the optic nerve is a region in 
which the rays of light make no impression, owing to the absence of the 
proper retinal elements ; the fibres of the optic nerve being insensible to the 
action of light. 

The course which a ray of light takes is as follows : After passing 
through the cornea, lens, and vitreous humor and the layers of the retina, 
it is finally arrested by the pigmentary layer of the choroid; here it excites, 
in the layer of rods and cones, some physical or chemical change, which 
is then transmitted to the fibres of the optic nerve, and thence to the brain, 
where it is perceived as a sensation of light. 

The Accommodation of the eye to vision for different distances is 
accomplished by a change in the convexities of the lens, caused by the 
action of the ciliary muscle. When the eye is accommodated for vision at 
far distances, the structures are in a passive condition and the lens is flat- 
tened; when it is adjusted for vision at short distances, the convexities of 
the lens, are increased. 

When the Ciliary muscle contracts and draws the choroid coat forward, 
the suspensory ligament is relaxed and the lens becomes more convex, in 
virtue of its own elasticity. 



THE SENSE OF SIGHT. Ill 

Optical Defects. Astigmatism is a condition of the eye which pre- 
vents vertical and horizontal lines from being focused at the same time, 
and is due to a greater curvature of the eye in one direction than another. 

Spherical aberration is a condition in which there is an indistinctness 
of an image from the unequal refraction of the rays, of light passing 
through the circumference and the centre of the lens ; it is corrected 
mainly by the iris, which cuts off the marginal rays, and only transmits 
those passing through the centre. 

Chromatic aberration, in which the image is surrounded by a colored 
margin, from the decomposition of the rays of light into their elementary . 
parts, is corrected by the different refractive powers of the transparent 
media in front of the retina. 

Myopia, or short-sightedness yis caused by an abnormal increase in the- 
antero-posterior diameter of the eyeball ; the lens, being too far removed 
from the retina, forms the image in front of it, and the perception becomes 
dim and blurred. Concave glasses correct this defect, by preventing the 
rays from converging too soon. 

Hypermetropia, or long-sightedness, is caused by a shortening of the 
antero-posterior diameter ; the lens consequently focuses the rays of light 
behind the retina. Convex glasses correct this defect, by converging the 
rays of light more anteriorly. 

Presbyopia is a loss of the power of accommodation of the eye to near 
objects, and usually occurs between the ages of 40 and 60; it is reme- 
died by the use of a convex eye-glass. 

Accessory Structures. The muscles which move the eyeball are 
six in number ; the superior and inferior recti, the external and internal 
recti, the superior and inferior oblique muscles. The four recti muscles, 
arising from the apex of the orbit, pass forward and are inserted into the 
sides of the sclerotic coat; the superior and inferior muscles rotate the 
eye around a horizontal axis ; the external and internal rotate it around 
a vertical axis. 

The superior oblique muscle, having the same origin, passes forward to 
the inner and upper angle of the orbital cavitv, where its tendon 
passes through a cartilaginous pulley ; it is then reflected backward and 
inserted into the sclerotic just behind the transverse diameter. Its function 
is to rotate the eyeball in- such a manner as to direct the pupil downward 
and outward. 

The inferior oblique muscle arises at the inner angle of tne orbit and 
then passes outward and backward to be inserted into the sclerotic. Its 
function is to rotate the eyeball and direct the pupil upward 'and outward. 



112 HUMAN PHYSIOLOGY. 

By the associated action of all these muscles, the eyeball is capable of 
performing all the varied and complex movements necessary for distinct 
vision. 

The Eyelids, bordered with short, stiff hairs, shade the eye and protect it 
from injury. On the posterior surface, just beneath the conjunctiva, are 
the Meibomian glands, which secrete an oily fluid ; it covers the edge of 
the lids and prevents the tears from flowing over the cheek. 

The Lachrymal Glands are ovoid in shape and situated at the upper 
and outer part of the orbital cavity; they open by from six to eight ducts 
at the outer portion of the upper lids. 

The Tears, secreted by the lachrymal glands, are distributed over the 
cornea by the lids during the act of winking, and keep it moist and free 
from dust. The excess of tears passes into the lachrymal ducts, which 
begin by two minute orifices, one on each lid, at the inner canthus. < They 
conduct the tears into the nasal duct, and so into the nose. 

THE SENSE OF HEARING. 

The Organ of Hearing is situated in the petrous portion of the tem- 
poral bone, and is divided into three portions, viz : the external ear, the 
middle ear and the internal ear. 

The External Ear consists of two portions, the pinna or auricle, and 
the external auditory canal. The former consisting of cartilage, which is 
irregularly folded and covered by integument, is united to the side of the head 
by ligaments and muscles ; the latter, partly cartilaginous and partly bony, 
is about one and a quarter inches in length ; it runs downward and forward 
from the concha to the middle ear, and is lined by a reflection of the gene- 
ral integument, in which is lodged a number of glands, which secrete the 
cerumen. 

The function of the external ear is to collect the waves of sound coming 
from all directions and to transmit them to the membrana tympani. 

The Middle Ear or Tympanum is an irregularly shaped cavity, 
narrow from side to side, but longer in its vertical and antero-posterior 
diameters. 

It is separated from the external ear by the membrana tympani, and 
from the internal ear by a second membrana tympani ; it communicates 
posteriorly with the mastoid cells, anteriorly with the pharynx, through 
the Eustachian tube. It is lined by mucous membrane, and contains three 
small bones, forming a connected chain running across its cavity. 

The Membrana tympani is a thin, delicate, translucent membrane, cir- 
cular in shape and measuring about two-fifths of an inch in diameter; it is 



THE SENSE OF HEARING. 113 

received into a delicate ring of bone, which in the adult becomes consoli- 
dated with the temporal bone ; it is concave externally and situated ob- 
liquely, inclining at an angle of 45 degrees. 

The membrane consists of three layers ; the outer is formed by a reflec- 
tion of the integument lining the external auditory canal; the middle is 
composed of fibrous tissue, and the internal of mucous membrane. 

The function of the membrana tympani is to receive and transmit the 
waves of sound to the chain of bones ; it is capable of being made tense 
and lax by the action of the tensor tympani and laxator tympani muscles, 
so as to vibrate in unison with the waves of sound in the external auditory 
meatus. When the membrane is relaxed, its vibrations have a greater 
amplitude, and it appreciates sounds of a low pitch. When it is made tense 
it vibrates less forcibly and appreciates sounds of a high pitch. 

The Chain of bones is formed by the malleus, incus and stapes, united 
together by ligaments. The ?nalleus consists of a head, neck, and handle, 
of which the latter is attached to the inner surface of the membrana tym- 
pani. The incus, or anvil bone, articulates with the head of the malleu 
by a capsular joint, and with the stapes by the end of its long process. 
The stapes resembles a stirrup in shape ; it articulates externally with the 
long process of the incus, and internally its oval base is applied to the 
edges of the foramen ovale. 

The function of the chain of bones is to transmit the waves of sound 
across the tympanum to the internal ear ; being surrounded by air, and act- 
ing as a solid rod, they prevent the vibrations from losing but little in in- 
tensity. 

The Tensor tympani muscle arises mainly from the cartilaginous part 
of the Eustachian tube ; it then passes backward into the tympanic cavity, 
where it bends at a right angle around a process of bone, and is inserted 
into the root of the handle of the malleus. Its function is to draw the 
handle of the malleus internally, and thus increases the tension of the 
membrana tympani, so as to make it capable of vibrating with sounds of 
greater or less intensity ; at the same time it tightens the joints of the 
chain of bones, so that they may the better conduct waves of sound to the 
internal ear, with but a slight loss of intensity. 

The Laxator tympani muscle, arising from the spinous process of the 
sphenoid bone, passes backward through the Glasserian fissure, into the 
tympanic cavity, and is inserted into the neck of the malleus. Its func- 
tion is to draw the handle of the malleus outward, and so relates the mem- 
brana tympani, and enables it to receive waves of sound of greater ampli- 
tude than when it is tense. 



114 HUMAN PHYSIOLQGY. 

The Stapedius muscle, emerging from the cavity of the pyramid of bone 
projecting from the posterior wall of the , tympanum, is inserted into the 
head of the stapes bone. Its function is to draw the stapes backward, 
preventing too great movement of the bone, and at the same time relaxing 
the membrana tympani. 

The Eustachian tube, by means of which the middle ear communicates 
with the pharynx, is partly bony and partly cartilaginous in its structure. 
It is about one and a half inches in length ; commencing at its opening in 
the pharynx, it passes upward and outward to the spine of the sphenoid 
bone, where it is slightly contracted ; it then gradually dilates as it passes 
backward into the tympanic cavity. It is lined by mucous membrane, 
which is continued into the middle ear and into the mastoid cells. 

The Eustachian tube permits the passage of air from the pharynx into 
the middle ear ; in this way the pressure of the air within and withput the 
membrana tympani is equalized, which is one of the essential conditions 
for the reception of sonorous vibrations. 

By closing the mouth and nose, and blowing out the cheeks, air can be 
forced into the middle ear, producing undue pressure, and bulging out of the 
membrana tympani ; by making an effort at swallowing, with the mouth 
and nose closed, the air in the tympanum can be rarefied and the tympanic 
membrane will be pressed in. In both such cases the acuteness of hearing 
is very 'much diminished. 

The pharyngeal orifice of the Eustachian tube is opened by the action 
of certain of the muscles of deglutition, viz : the levator palati, tensor 
palati, and at times the palato-pharyngei muscles. 

The Internal Ear, or Labyrinth, is located in the petrous portion 
of the temporal bone, and consists of an osseous and membranous portion. 

The Osseous Labyrinth is divisible into three parts, viz : the vesti- 
bule, the semi-circular canals, and the cochlea. 

The Vestibule is a small, triangular cavity, which communicates with 
the middle ear by the foramen ovale ; in the natural condition it is closed 
by the base of the stapes bone. The filaments of the auditory nerve enter 
the vestibule through small foramina in the inner wall, at the fovea hemi- 
spherica. 

The Semi-circular canals are three in number ; the superior vertical, 
the inferior vertical and the horizontal, each of which opens into the cavity 
of the vestibule, by two openings, with the exception of the two vertical, 
which at one extremity open by a common orifice. 

The Cochlea forms the anterior part of the internal ear. It is a gradu- 



THE SENSE OF HEARING. 115 

ally tapering canal, about one and a half inches in length, which winds 
spirally around a central axis, the modiolus, two and a half times. The 
interior of the cochlea is partly divided into two passages by a thin plate of 
bone, the lamina osseous spiralis, which projects from the central axis two- 
thirds across the canal. These passages are termed the scala vestibuli and 
the scala tympani, from their communication with the vestibule and tym- 
panum. The scala tympani communicates with the middle ear through 
the foramen rotundum, which, in the natural condition, is closed by the 
second membrana tympani ; superiorly they are united by an opening, 
the helicotrema. 

The whole interior of the labyrinth, the vestibule, the semi-circular 
canals, and the scala of the cochlea, contains a clear, limpid fluid, the peri- 
lymph, secreted by the periosteum lining the osseous walls. 

The Membranous Labyrinth corresponds to the osseous labyrinth 
with respect to form, though somewhat smaller in size. 

The Vestibular portion consists of two small sacs, the utricle and saccule. 
The Semi-circular canals communicate with the utricle in the same 
manner as the bony canals communicate with the vestibule. The saccule 
communicates with the membranous cochlea by the canalis reuniens. In 
the interior of the utricle and saccule, at the entrance of the auditory, 
nerve, are small masses of carbonate of lime crystals, constituting the otoliths. 
Their function is unknown. 

The Membranous cochlea is a closed tube, commencing by a blind ex- 
tremity at the first turn of the cochlea, and terminating at its apex by a 
blind extremity also. It is situated between the edge of the osseous lamina 
spiralis and the outer wall of the bony cochlea, and follows it in its turns 
around the modiolus. 

A transverse section of the cochlea shows that it is divided into two 
portions by the osseous lamina and the basilar membrane : I . The scala ves- 
tibuli, bounded by the periosteum and membrane of Reissner. 2. The scala 
tympani, occupying the inferior portion, and bounded above by the septum, 
composed of the osseous lamina and the membrana basilaris. 

The true membranous canal is situated between the membrane of Reiss- 
ner and the basilar membrane. It is triangular in shape, but is partly 
divided into a triangular portion and a quadrilateral portion by the tectorial 
membrane. 

The Organ of Corti is situated in the quadrilateral portion of the canal, 
and consists of pillars or rods, of the consistence of cartilage. They are 
arranged in two rows ; one internal, the other external ; these rods rest upon 
the basilar membrane ; their bases are separated from each other, but their 



116 HUMAN PHYSIOLOGY. 

upper extremities are united, forming an arcade. In the internal row it 
is estimated there are about 3500, and in the external row about 5200 of 
these rods. 

On the inner side of the internal row is a single layer of elongated hair 
cells ; on the outer surface of the external row are three such layers of hair 
cells. Nothing definite is known as to their function. 

The Endolymph occupies the interior of the utricle, saccule, membran- 
ous canals, and bathes the structures in the interior of the membranous 
cochlea, throughout its entire extent. 

The Auditory Nerve at the bottom of the internal auditory meatus 
divides into (1) a vestibular branch, which is distributed to the utricle and 
semi-circular canals; (2) a cochlear branch, which passes into the central 
axis at its base, and ascends to its apex ; as it ascends, fibres are given off, 
which pass between the plates of the osseous- lamina, to be ultimately con- 
nected with the organ of Corti. 

The Function of the semi-circular canals appears to be to assist in main- 
taining the equilibrium of the body; destruction of the vertical canal is 
followed by an oscillation of the head upward and downward ; destruc- 
tion of the horizontal canal is followed by oscillations from left to right. 
When the canals are injured on both sides, the animal loses the power of 
maintaining equilibrium upon making muscular movements. 

Function of the Cochlea. It is regarded as possessing the power of 
appreciating the quality of pitch and the shades of different musical tones. 
The elements of the organ of Corti are analagous, in some respects, to 
a musical instrument, and are supposed, by Helmholtz, to be tuned so as 
to vibrate in unison with the different tones conveyed to the internal ear. 

Summary. The waves of sound are gathered together by the pinna 
and external auditory meatus, and conveyed to the membrana tympani. 
This membrane, made tense or lax by the action of the tensor tympani 
and laxator tympani muscles, is enabled to receive sound waves of either 
a high or low pitch. The vibrations are conducted across the middle ear 
by the chain of bones to the foramen ovale, and by the column of air to 
the tympanum, to the foramen rotundum, which is closed by the second 
membrana tympani ; the pressure of the air in the tympanum being regu- 
lated by the Eustachian tube. 

The internal ear finally receives the vibrations which excite vibrations 
successively in the perilymph, the walls of the membranous labyrinth, the 
endolymph, and, lastly, the terminal filaments of the auditory nerve, by 
which they are conveyed to the brain. 



VOICE AND SPEECH. 117 

VOICE AND SPEECH. 

The Larynx is the organ of voice. Speech is a modification of voice, 
and is produced by the teeth, and the muscles of the lips and tongue, 
coordinated in their action by stimuli derived from the cerebrum. 

The Structures entering into the formation of the larynx are mainly 
the thyroid, cricoid, and arytenoid cartilages ; they are so situated and 
united by means of ligaments and muscles as to form a firm cartilaginous . 
box. The Larynx is covered externally by fibrous tissue and lined inter- 
nally with mucous membrane. 

The Vocal Cords are four ligamentous bands, running antero-posteri- 
orly across the upper portion of the larynx, and are divided into the two 
superior, or false vocal cords, and the two inferior or true vocal cords ; 
they are attached anteriorly to the receding angle of the thyroid cartilages 
and posteriorly to the anterior part of the base of the arytenoid cartilages. 
The space between the true vocal cords is the glottis, or rima glottidis. 

The Muscles which have a direct action upon the movements of the 
vocal cords are nine in number, and take their names from their points of 
origin and insertion, viz : the two eric o -thyroid, two thy ro- arytenoid, two 
posterior crico-arytenoid, two lateral crico- arytenoid, and one arytenoid 
muscles. 

The crico-thyroid muscles, by their contraction, render the vocal cords 
more tense by drawing up the anterior portion of the cricoid cartilage and 
approximating it to the thyroid, and at the same time tilting the posterior 
portion of the cricoid and arytenoid cartilages backward. 

The thyro-arytenoid, by their contraction relax the vocal cords by draw- 
ing the arytenoid cartilage forward and the thyroid backward. 

The posterior crico-arytenoid muscles, by their contraction rotate the 
arytenoid cartilages outward and thus separate the vocal cords and enlarge 
the aperture of the glottis. They principally aid the respiratory move- 
ments during inspiration. 

The lateral crico-arytenoid muscles are antagonistic to the former, and 
by their contraction rotate the arytenoid cartilages so as to approximate 
the vocal cords and constrict the glottis. 

The arytenoid muscle assists in the closure of the aperture of the glottis. 

The inferior laryngeal nerve animates all the muscles of the larynx, 
with the exception of the crico-thyroid. 

Movements of the Vocal Cords. During respiration the move- 
ments of the vocal cords differ from those occurring during the production 
of voice. 



118 HUMAN PHYSIOLOGY. 

At each inspiration, the true vocal cords are widely separated, and the 
aperture of the glottis is enlarged by the action of the crico-arytenoid mus- 
cles, which rotate outwards the anterior angle of the base of the arytenoid 
cartilages ; at each expiration the larynx becomes passive ; the elasticity 
of the vocal cords returns them to their original position and the air is 
forced out by the elasticity of the lungs and walls of the thorax. 

Phonation. As soon as phonation is about to be accomplished a marked 
change in the glottis is noticed with -the aid of the laryngoscope. The 
true vocal cords suddenly become approximated and are made parallel, 
giving to the glottis the appearance of a narrow slit, the edges of which 
are capable of vibrating accurately and rapidly ; at the same time their 
tension is much increased. 

With the vocal cords thus prepared, the expiratory muscles force the 
column of air into the lungs and trachea through the glottis, throwing 
the edges of the cords into vibration. 

The pitch of sounds depends upon the extent to which the vocal cords 
are made tense and the length of the aperture through which the air 
passes. In the production of sounds of a high pitch the tension of the 
vocal cords becomes very marked, and the glottis diminishes in length. 
When grave sounds, having a low pitch, are emitted from the larynx, the 
vocal cords are less tense and their vibrations are large and loose. 

The quality of voice depends upon the length, size, and thickness of 
the cords, and the size, form and construction of the trachea, larynx and 
the resonant cavities of the pharynx, nose and mouth. 

The compass of the voice comprehends from two to three octaves. The 
range is different in the two sexes ; the lowest note of the male being 
about one octave lower than the lowest note of the female ; while the 
highest note of the male is an octave less than the highest of the female. 
The varieties of voices, e. g., bass, baritone, tenor, contralto, mezzo- 
soprano, and soprano, are due to the length of the vocal cords; being 
longer when the voice has a low pitch, and shorter when it has a high pitch. 
Speech is the faculty of expressing ideas by means of combinations of 
sounds, in obedience to the dictates of the cerebrum. 

Articulate sounds may be divided into vowels and consonants. The 
vowel sounds, a, e, i, o, u, are produced in the larynx by the vocal cords. 
The consonantal sounds are produced in the air passages above the larynx 
by an interruption of the current of air by the lips, tongue, and teeth ; the 
consonants may be divided into : (i) mutes, b, d, k, p, t, c,g; (2) dentals, 
dyjy s, t, % ; (3) nasals, m, n, ng ; (4) labials, b, p,f, v f m ; (5) gutturals, 
k,g, c t and g hard; (6) liquids, /, m, n, r. 



REPRODUCTION. 119 

REPRODUCTION. 

Reproduction is the function by which the species is preserved, and is 
accomplished by the organs of generation in the two sexes. 

GENERATIVE ORGANS OF THE FEMALE, 

The Generative Organs of the Female consist of the ovaries, Fal- 
lopian tubes, uterus and vagina. 

The Ovaries are two small, ovoid, flattened bodies, measuring one 
inch and a half in length, and three-quarters of an inch in width ; they are 
situated in the cavity of the pelvis, and imbedded in the posterior layer of 
the broad ligament ; attached to the uterus by a round ligament, and to 
the extremities of the Fallopian tubes by the fimbriae. The ovary 
consists of an external membrane of fibrous tissue, the cortical portion, 
in which are imbedded the Graafian vesicles, and an internal portion, 
the stroma, , containing blood vessels. 

The Graafian Vesicles are exceedingly numerous, but situated only 
in the cortical portion. Although. the ovary contains the vesicles from 
the period of birth, it is only at the period of puberty that they attain their 
full development. From this time onward to the catamenial period there 
is a constant growth and maturation of the Graafian vesicles. They consist 
of an external investment, composed of fibrous tissue and blood vessels, in 
the interior of which is a layer of cells, forming the membrana granulosa ; 
at its lower portion there is an accumulation of cells, the proligerous disc, 
in which the ovum is contained. The cavity of the vesicle contains a 
slightly-yellowish, alkaline, albuminous fluid. 

The Ovum is a globular body, measuring about the y^th of an inch 
in diameter ; it consists of an external investing membrane, the vitelline 
membrane, a central granular substance, the vitellus, or yelk, a nucleus, 
the germinal vesicle, in the interior of which is imbedded the nucleolus, 
or germinal spot. 

The Fallopian Tubes are about four inches in length, and extend 
outward from the upper angles of the uterus, between the folds of the 
broad ligaments, and terminate in a fringed extremity, which is attached 
by one of the fringes to the ovary. They consist of three coats; (i) the 
external, or peritoneal, (2) middle, or muscular, the fibres of which are 
arranged in a circular and longitudinal direction, (3) internal, or mucous, 
covered with ciliated epithelial cells, which are always waving from the 
ovary toward the uterus. 



120 HUMAN PHYSIOLOGY. 

The Uterus is pyriform in shape, and may be divided into a body 
and neck ; it measures about three inches in length and two inches in 
breadth in the unimpregnated state. At the lower extremity of the neck 
is the os externum ; at the junction of the neck with the body is a constric- 
tion, the os internum. The cavity of the uterus is triangular in shape, the 
walls of which are almost in contact. 

The walls of the uterus are made up of several layers of non-striated 
muscular fibres, covered externally by peritoneum, and lined internally by 
mucous membrane, containing numerous tubular glands, and covered by- 
ciliated epithelial cells. 

The Vagina is a membranous canal, from five to six inches in length, 
situated between the rectum and bladder. It extends obliquely upward 
from the surface, almost to the brim of the pelvis, and embraces at its 
upper extremity the neck of the uterus. N 

Discharge of the Ovum. As the Graafian vesicle matures, it in- 
creases in size, from an augmentation of its liquid contents, and approaches 
the surface of the ovary, where it forms a projection, measuring from one- 
fourth to one-half an inch in size. The maturation of the vesicle occurs 
periodically, about every 28 days, and is attended by the phenomena of 
menstruation. During this period of active congestion of the reproductive 
organs, the Graafian vesicle ruptures, the ovum and liquid contents escape, 
and are caught by the fimbriated extremity of the Fallopian tube, which 
has adapted itself to the posterior surface of the ovary. The passage of 
the ovum through the Fallopian tube into the uterus occupies from ten to 
fourteen days, and is accomplished by muscular contraction and the action 
of the ciliated epithelium. 

Menstruation is a periodical discharge of blood from the mucous mem- 
brane of the uterus, due to a fatty degeneration of the small blood ves- 
sels. Under the pressure of an increased amount of blood in the repro- 
ductive organs, attending the process of ovulation, the blood vessels 
rupture, and a hemorrhage takes place into the uterine cavity ; thence it 
passes into the vagina, where it is kept in a fluid condition from admixture 
with the vaginal mucus. Menstruation lasts from five to six days, and the 
amount of blood discharged averages about five ounces. 

Corpus Luteum. For some time anterior to the rupture of a Graa- 
fian vesicle, it increases in size, and becomes vascular; its walls become 
thickened, from the deposition of a reddish-yellow, glutinous substance, a 
product of cell growth from the proper coat of the follicle and the membrana 
granulosa. After the ovum escapes, there is usually a small effusion of 



REPRODUCTION. 



121 



blood into the cavity of the follicle, which soon coagulates, loses its coloring 
matter, and acquires the characteristics of fibrin, but it takes no part in the 
formation of the corpus luteum. The walls of the follicle become convo- 
luted, vascular, and undergo hypertrophy, until they occupy the whole of 
the follicular cavity. At its period of fullest development, the corpus 
luteum measures three-fourths of an inch in length and one-half inch in 
depth. In a few weeks the mass loses its red color, and becomes yellow, 
constituting the corpus luteum , or yellow body. It then begins to retract, 
and becomes pale ; and at the end of two months nothing remains but a 
small cicatrix upon the surface of the ovary. Such are the changes in the 
follicle, if the ovum has not been impregnated. 

The corpus luteum, after impregnation has taken place, undergoes a much 
slower development, becomes larger, and continues during the entire 
period of gestation. The differences between the corpus luteum of the 
unimpregnated and pregnant condition is expressed in the following table 
by Dalton : — ■ 

Corpus Luteum of Menstruation. Corpus Luteum of Pregnancy. 

Three-quarters of *an inch in diameter; central clot 
reddish ; convoluted wall pale. 

Smaller ; convoluted | Larger ; convoluted wall 
wall bright yellow ; clot bright yellow ; clot still red- 
still reddish. 

Reduced to the condi- 
tion of an insignificant 
cicatrix. 



At the end of 
three weeks. 
One month. 



Two months. 



. Four months. 



Six months. 



Nine months. 



Absent 
able. 



Absent. 



Absent. 



or unnotice- 



dish. 

Seven- eighths of an inch 
in diameter ; convoluted wall 
bright yellow; clot perfectly 
decolorized. 

Seven-eighths of an inch 
in diameter; clot pale and 
fibrinous ; convoluted wall 
dull yellow. 

Still as large as at the end 
of second month; clot fib- 
rinous ; convoluted wall 
paler. 

Half an inch in diameter ; 
central clot converted into a 
radiating cicatrix ; external 
wall tolerably thick and 
convoluted, but without any 
bright yellow color. 



122 HUMAN PHYSIOLOGY. 

GENERATIVE ORGANS OF THE MALE. 

The Generative Organs of the Male consist of the testicles, vasa 
deferentia, vesiculse seminales and penis. 

The Testicles, the essential organs of reproduction in the male, are 
two oblong glands, about an inch and a half in length, compressed from 
side to side, and situated in the cavity of the scrotum. 

The proper coat of the testicle, the tunica albuginea, is a white, fibrous 
structure, about the S^th °f an i ncn m thickness; after enveloping the 
testicle, it is reflected into its interior at the posterior border, and forms a 
vertical process, the mediastinum testis, from which septa are given off, 
dividing the testicle in lobules. 

The substance of the testicle is made up of the seminiferous tubules, 
which exist to the number of 840; they are exceedingly convoluted, and 
when unraveled, are about 30 inches in length. As they pass towards the 
apices of the lobules they become less convoluted and terminate in from 20 
to 30 straight ducts, the vasa recta, which pass upward through the medias- 
tinum and constitute the rete testis. At the upper part of the mediastinum 
the tubules unite to form from 9 to 30 small ducts, the vasa efferentia, which 
become convoluted, and form the globus major of the epididymis ; the 
continuation of the tubes downward behind the testicle and a second con- 
volution, constitutes the body and globus minor. 

The seminal tubule consists of a basement membrane lined by granular 
nucleated epithelium. 

The Vas Deferens, the excretory duct of the testicle, is about two 
feet in length, and may be traced upward from the epididymis to the under 
surface of the base of the bladder, where it unites with the duct of the vesi- 
cula seminalis, to form the ejaculatory duct. 

The Vesiculse Seminales are two lobulated, pyriform bodies, about 
two inches in length, situated on the under surface of the bladder. 

They have an external fibrous coat, a middle muscular coat, and an in- 
ternal mucous coat, covered by epithelium, which secretes a mucous fluid. 
The vesicube seminales serve as reservoirs, in which the seminal fluid is 
temporarily stored up. • 

The Ejaculatory Duct, about j£ of an inch in length, opens into the 
urethra and isformed by the union of the vasa deferentia and the ducts of 
the vesicular seminales. 

The Prostate Gland surrounds the posterior extremity of the urethra, 
and opens into it by from twenty to thirty openings, the orifices of the pros- 
tatic tubules. The gland secretes a fluid which forms part of the semen, 
and assists in maintaining the vitality of the spermatozoa. 



DEVELOPMENT. 123 

Semen is a complex fluid, made up of the secretions from the testicles, 
the vesiculse seminales, the prostatic and urethral glands. It is greyish- 
white in color, mucilaginous in consistence, of a characteristic odor, and 
somewhat heavier than water. From half a drachm to a drachm is 
ejaculated at each orgasm. 

The Spermatozoa are peculiar anatomical elements, developed within 
the seminal tubules, and possess the power of spontaneous movement. 
The spermatozoa consist of a conoidal head and a long filamentous tail, 
which is in continuous and active motion ; as long as they remain in the 
vas deferens they are quiescent, but when free to move in the fluid of the 
vesiculae seminales, become very active. 

Origin, The spermatozoa appear at the age of puberty, and are then 
constantly formed until an advanced age. ■ They are developed from the 
nuclei of large, round cells, contained in the interior of the seminal tub- 
ules, as many as fifteen to twenty developing in a single ceil. 

When the spermatozoa are introduced into the vagina, they pass readily 
into the uterus and through the Fallopian tubes towards the ovaries, where 
they remain and retain their vitality for a period of from 8 to 10 days. 

Fecundation is the union of the spermatozoa with the ovum during 
its passage towards the uterus, and usually takes place in the Fallopian 
tube, just outside of the womb. After floating around the ovum in an 
active manner, they penetrate the vitelline membrane, pass into the interior 
of the vitellus, where they lose their vitality, and along with the germinal 
vesicle entirely disappear. 

DEVELOPMENT OF ACCESSORY STRUCTURES. 

Segmentation of the Vitellus. After the disappearance of the 
spermatozoa and the germinal vesicle, there remains a transparent granular, 
albuminous substance, in the centre of which a new nucleus soon appears ; 
this constitutes the parent cell, and is the first stage in the development of 
the new being. 

Following this, the vitellus undergoes segmentation ; a constriction ap- 
pears on the opposite sides of the vitellus, which gradually deepens, until 
the yelk is divided into two segments, each of which has a distinct nucleus 
and nucleolus ; these two segments undergo a further division into four, 
the four into eight, the eight into sixteen, and so on, until the entire vitellus 
is divided into a great number of cells, each of which contains a nucleus 
and nucleolus. 

The peripheral cells of this "mulberry mass" then arrange themselves 
so as to form a membrane, and as they are subjected to mutual pressure, 



124 HUMAN PHYSIOLOGY. 

assume a polyhedral shape, which gives to the membrane a mosaic appear- 
ance. The central part of the vitcllus becomes filled with a clear fluid. 
A secondary membrane shortly appears within the first, and the two 
together constitute the external and internal blastodermic membranes. 

Germinal Area. At about this period there is an accumulation of 
cells at a certain spot upon the surface of the blastodermic membranes, 
which marks the position of the future embryo. This spot, at first circular, 
soon becomes elongated, and forms the primitive trace, around which is a 
clear space, the area pellucida, which is itself surrounded by a darker 
region, the area opaca. 

The primitive trace soon disappears, and the area pellucida becomes 
guitar-shaped; a new groove, the medullary groove, is now formed, which 
develops from before backward,, and becomes the neural canal. 

Blastodermic Membranes. The embryo, at # this period, consists of 
three layers, viz : the external and internal blastodermic membranes, and 
a middle membrane formed by a genesis of cells from their internal sur- 
faces. These layers are known as the epiblast, mesoblast, and hypoblast. 

The Epiblast gives rise to the central nervous system, the epidermis of 
the skin and its appendages, and the primitive kidneys. 

The Mesoblast gives rise to the dermis, muscles, bones, nerves, blood 
vessels, sympathetic nervous system, connective tissue, the urinary and 
reproductive apparatus and the walls of the alimentary canal. 

The Hypoblast gives rise to the epithelial lining of the alimentary canal 
and its glandular appendages, the liver and pancreas, and the epithelium 
of the respiratory tract. 

Dorsal Laminae. As development advances, the true medullary groove 
deepens, and there arise two longitudinal elevations of the epiblast, the 
dorsal lamina, one on either side of the groove, which grow up, arch 
over and unite so as to form a closed tube, the primitive central nervous 
system. 

The Chorda Dorsalis is a cylindrical rod running almost throughout 
the entire length of the embryo. It is formed by an aggregation of meso- 
blastic cells, and situated immediately beneath the medullary groove. 

Primitive Vertebrae. On either side of the neural canal the cells of 
the mesoblast undergo a longitudinal thickening, which develops and 
extends around the neural canal and the chorda dorsalis, and forms the 
arches and bodies of the vertebrae. They become divided transversely 
into four-sided- segments. 

The Mesoblast now separates into two layers; the external joining with 



DEVELOPMENT. 125 

the epibiast forms the somatopleure ; the internal, joining with the hypo- 
blast, forms the splanchnopleure ; the space between them constituting the 
pleuro-peritoneal cavity. 

Visceral Laminae. The walls of the pleuro-peritoneal cavity are 
formed by a downward prolongation of the somatopleure (the visceral 
lamina), which, as they extend around in front, pinch off a portion of the 
yelk sac (formed by the splanchnopleure), which becomes the primitive 
alimentary canal ; the lower portion, remaining outside of the body cavity, 
forms the umbilical vesicle, which after a time disappears. 

Formation of Foetal Membranes. The Amnion appears shortly 
after the embryo begins to develop, and is formed by folds of the epibiast 
and external layer of the mesoblast, rising up in front and behind, and on 
each side ; these amniotic folds gradually extend over the back of the 
embryo to a certain point, where they coalesce, and enclose a cavity, the 
amniotic cavity. The membranous partition between the folds disappears, 
and the outer layer recedes and becomes blended with the. vitelline mem- 
brane, constituting the chorion, the external covering of the embryo. 

The Allantois. As the amnion develops, there grows out from the 
posterior portion of the alimentary canal a pouch, or diverticulum, the 
allantois, which carries blood vessels derived from the intestinal circula- 
tion. As it gradually enlarges, it becomes more vascular, and inserts 
itself between the two layers of the amnion, coming into intimate contact 
with the external layer. Finally, from increased growth, it completely 
surrounds the embryo, and its edges become fused together. 

In the bird, the allantois is a respiratory organ, absorbing oxygen and 
exhaling carbonic acid; it also absorbs nutritious matter from the interior 
of the egg. 

Amniotic fluid. The amnion, when first formed, is in close contact 
with the surface of the ovum ; but it soon enlarges, and becomes filled 
with a clear, transparent fluid, containing albumen, glucose, fatty matters, 
urea and inorganic salts. It increases in amount up to the latter period of 
gestation, when it amounts to about two pints. In the space between the 
amnion and allantois is a gelatinous material, which is encroached upon, 
and finally disappears as the amnion and allantois come in contact, at 
about the fifth month. 

The Chorion, the external investment of the embryo, is formed by a 
fusion of the original vitelline membrane, the external layer of the amnion, 
and the allantois. The external surface now becomes covered with villous 
processes, which increa c e in number and size by the continual budding 



126 HUMAN PHYSIOLOGY. 

and growth of club-shaped processes from the main stem, and give to the 
chorion a shaggy appearance. They consist of a homogeneous, granular 
matter, and are penetrated by branches of the blood vessels derived from 
the aorta. 

The presence of villous processes in the uterine cavity is proof positive 
of the previous existence of a foetus. They are characteristic of the 
chorion, and are found under no other circumstances. 

At about the end of the second month, the villosities begin to atrophy and 
disappear from the surface of the chorion, with the exception of those situated 
at the points of entrance of the foetal blood vessels, which occupy about 
one-third of its surface, where they continue to grow longer, become more 
vascular, and ultimately assist in the formation of the placenta ; the re- 
maining two-thirds of the surface loses its villi and blood vessels, and 
becomes a simple membrane. 

The Umbilical Cord, connects the foetus with that portion of the 
chorion whkh forms the foetal side of the placenta. It is a process of the 
allantois, and contains two arteries and a vein, which have a more or less 
spiral direction. It appears at the end of the first month, and gradually 
increases in length, until at the end of gestation it measures about 20 
inches. The cord is also surrounded by a process of the amnion. 

Development of the Decidual Membrane. The interior of the 
uterus is lined by a thin, delicate mucous membrane, in which are im- 
bedded immense numbers of tubules, terminating in blind extremities, the 
uterine tubules. At each period of menstruation the mucous membrane 
oecomes thickened and vascular, which condition, however, disappears 
after the usual menstrual discharge. When the ovum becomes fecundated, 
the mucous membrane takes on an increased growth, becomes more hyper- 
trophied and vascular, sends up little processes, or elevations from its sur- 
face, and constitutes the decidua vera. 

As the ovum passes from the Fallopian tube into the interior of the 
uterus, the primitive vitelline membrane, covered with villosities, becomes 
entangled with the processes of the mucous membrane. A portion of the 
decidua vera then grows up on all sides, and encloses the ovum, forming 
the decidua reflexa, while the villous processes of the chorion insert them- 
selves into the uterine tubules, and in the mucous membrane between them. 

As development advances the decidua reflexa increases in size, and at 
about the end of the fourth month comes in contact with the decidua vera 
with which it is ultimately fused. 

The Placenta. Of all the embryonic structures, the placenta is the 



DEVELOPMENT. 127 

most important. It begins to be formed towards the end of the second 
month, and then increases in size until the end of gestation, when it assumes 
an oval or rounded shape, and measures from 7 to 9 inches in length, 6 to 8 
inches in breadth, and weighs from 15 to 20 ounces. It is most frequently 
situated at the upper and posterior part of the inner surface of the uterus. 
The placenta consists of two portions, a fcetal and a maternal. 
The Fcetal portion is formed by the villi of the chorion, which by devel- 
oping, rapidly increase in size and number. They become branched and 
penetrate the uterine tubules, which enlarge and receive their many rami- 
fications. The capillary blood vessels in the interior of the villi also en- 
large and freely anastomose with each other. 

The Maternal portion is formed from that part of the hypertrophied and 
vascular decidual membrane between the ovum and the. uterus, the decidua 
serotina. As the placenta increases in size, the maternal blood vessels 
around the tubules become more and more numerous, and gradually fuse 
together, forming great lakes, which constitute sinuses in the walls of the 
uterus. 

As the latter period of gestation approaches, the villi extend deeper into 
the decidua, while the sinuses in the maternal portion become larger and 
extend further into the chorion. Finally, from excessive development of 
the blood vessels, the structures between them disappear, and as their walls 
come in contact, they fuse together, so that, ultimately, the maternal and 
foetal blood are only separated by a thin layer of a homogeneous substance. 
When fully formed, the placenta consists principally of blood vessels inter- 
lacing in every direction. The blood of the mother passes from the ute- 
rine vessels into the lakes surrounding the villi ; the blood from the child 
flows from the umbilical arteries into the interior of the villi ; but there is 
not at any time an intermingling of blood, the two being separated by a 
delicate membrane formed by a fusion of the walls of the blood vessels and 
the walls of the villi and uterine sinuses. 

The function of the placenta is that of a respiratory organ, permitting 
the oxygen of the maternal blood to pass by osmosis through the delicate 
placental membrane into the blood of the foetus ; at the same time the car- 
bonic acid and other waste products, the result of nutritive changes in the 
foetus, are discharged into the maternal blood, and so carried to the vari- 
ous eliminating organs. 

Through the placenta also, passes all the nutritious materials of the ma- 
ternal blood which are essential for the development of the embryo. 

At about the middle of gestation there develops beneath the decidual 
membrane a new mucous membrane, destined to perform the functions of 



128 HUMAN PHYSIOLOGY. 

the old when it is extruded from the womb, along with the other embry- 
onic structures, during parturition. 

DEVELOPMENT OF THE EMBRYO. 

Nervous System. The cerebro-spinal axis is formed within the medul- 
lary canal by the development of cells from its inner surfaces, which as they 
increase fill up the canal, and there remains only the central canal of the 
cord. The external surface gives rise to the dura mater and pia mater. 
The neural canal thus formed is a tubular membrane ; it terminates pos- 
teriorly in an oval dilatation, and anteriorly in a bulbous extremity, which 
soon becomes partially contracted, and forms the anterior, middle, and 
posterior cerebral vesicles, from which are ultimately developed the cere- 
brum, the corpora quadrigemina, and medulla oblongata, respectively. 

The anterior vesicle soon subdivides into two secondary vesicles, the larger 
of which becomes the hemispheres, the smaller, the optic thalami ; the 
posterior vesicle also divides into two ; the anterior becoming the cere- 
bellum, the posterior, the pons Varolii and medulla oblongata. 

About the seventh week the straight chain of cerebral vesicles becomes 
curved from behind forward and forms three prominent angles. As devel- 
opment advances, the relative size of the encephalic masses changes. The 
cerebrum developing more rapidly than the posterior portion of the brain, 
soon grows backward and arches over the optic thalami and the tubercula 
quadrigemina ; the cerebellum overlaps the medulla oblongata. 

The surface of the cerebral hemispheres is at first smooth, but at about 
the fourth month begins to be marked by the future fissures and convolu- 
tions. 

The Eye is formed from a little bud projecting from the side of the 
anterior vesicle. It is at first hollow, but becomes lined with nervous 
matter, forming the optic nerve and retina ; the remainder of the cavity is 
occupied by the vitreotis body. The anterior portion of the pouch be- 
comes invaginated and receives the crystalline lens, which is a product 
of the epiblast, as is also the cornea. The iris appears as a circular 
membrane without a central aperture, about the seventh week ; the eyelids 
are formed between the second and third months. 

The Internal Ear is developed from the auditory vesicle, budding 
from the third cerebral vesicle ; the membranous vestibule appears first, 
and from it diverticula are given off, which become the semi-circular canals 
and cochlea. 

The cavity of the tympanum, the Eustachian tube, and the external audi- 
tory canal are the remains of the first branchial cleft ; the cavity of this 



DEVELOPMENT OF THE EMBRYO. 129 

cleft being subdivided into the tympanum and external auditory meatus by 
the membrana tympani. 

The Skeleton. The chorda dorsalis, the primitive part of the verte- 
bral column, is a cartilaginous rod situated beneath the medullary groove. 
It is a temporary structure, and disappears as the true bony vertebrae de- 
velop. On either side are the quadrate masses of the mesoblast, the primi- 
tive vertebrae, which send processes upward and around the medullary 
groove, and downward and around the chorda dorsalis, forming in these 
situations the arches and bodies of the future vertebrae. 

More externally the outer layer of the mesoblast and epiblast arch down- 
ward and forward, forming the ventral laminae, in which develop the mus- 
cles and bones of the abdominal walls. 

The true cranium is an anterior development of the vertebral column, 
and consists of the occipital, parietal and frontal segments, which corres- 
pond to the three cerebral vesicles. The base of the cranium consists at 
this period, of a cartilaginous rod on either side of the anterior extremity 
of the chorda dorsalis, in which three centres of ossification appear, the 
basi- occipital, the basi-sphenoidal, and the pre-sphenoidal. They ultimately 
develop into the basilar process of the occipital bone and the body of the 
sphenoid. 

The entire skeleton is at first either membranous or cartilaginous. At 
the beginning of the second month centres of ossification appear in the 
jaws and clavicle ; as development advances, the ossific points in all the 
future bones extend, until ossification is completed. 

The limbs develop from four little buds projecting from the sides of the 
embryo, which, as they increase in length, separate into the thigh, leg and 
foot, and the arm, forearm and hand ; the extremities of the limbs undergo 
subdivision, to form the fingers and toes. 

Face and Visceral Arches. In the facial and cervical regions the 
visceral laminae send up three processes, the' visceral arches, separated by 
clefts, the visceral clefts. 

The first, or the mandibular arches, unite in the median line to form the 
lower jaw, and superiorly form the malleus. A process jutting from its 
base grows forward, unites with the fronto-nasal process growing from 
above, and forms the upper jaw. When the superior maxillary processes 
fail to unite, there results the cleft palate deformity; if the integument also 
fails to unite, there results the hare-lip deformity. The space above the 
mandibular arch becomes the mouth. 

The second arch develops the incus and stapes bones, the styloid process 
and ligament, and the lesser cornu of the hyoid bone. The cleft between the 



130 HUMAN PHYSIOLOGY. 

first and second arches partially closes up, but there remains an opening a 
the side which becomes the Eustachian tube, tympanic cavity, and external 
auditory meatus. 

The third arch develops the body and greater cornu of the hyoid bone. 

Alimentary Canal and its Appendages. The alimentary canal is 
formed by a pinching off of the yelk sac by the visceral plates as they 
grow downward and forward. It consists of three distinct portions, the 
fore gut, the hind gut, and the central part, which communicates for 
some time with the yelk sac. It is at first a straight tube, closed at both 
extremities, lying just beneath the vertebral column. The canal gradu- 
ally increases in length, and becomes more or less convoluted ; at its ante- 
rior portion two pouches appear, which become the cardiac and pyloric 
extremities of the stomach. At about the seventh week the inferior 
extremity of the intestine is brought into communication with the exte- 
rior, by an opening, the anus. Anteriorly the mouth and pharynx are 
formed by an involution of epiblast, which deepens until it communicates 
with the fore gut. 

The Liver appears as a slight protrusion from the sides of the alimen- 
tary canal, about the end of the first month ; it grows very rapidly, attains 
a large size, and almost fills up the abdominal cavity. The hepatic cells 
are derived from the intestinal epithelium, the vessels and connective 
tissue from the mesoblast. 

The Pancreas is formed by the hypoblastic membrane. It originates in 
two small ducts budding from the duodenum, which divide and subdivide, 
and develop the glandular structure. 

The Ltings are developed from the anterior part of the oesophagus. At 
first a small bud appears, which, as it lengthens, divides into two branches ; 
secondary and tertiary processes are given off these, which form the bron- 
chial tubes and air cells. The lungs originally extended into the abdomi- 
nal cavity, but became confined to the thorax by the development of the 
diaphragm. 

The Bladder is formed by a dilatation of that portion of the allantois 
remaining within the abdominal cavity. It is at first pear-shaped, and 
communicates with the intestine, but later becomes separated, and opens 
exteriorly by the urethra. It is attached to the abdominal walls by a 
rounded cord, the urachus, the remains of a portion of the allantois. 

Genito-Urinary Apparatus. The Wolffian bodies appear about the 
thirtieth day, as long hollow tubes running along each side of the primi- 
tive vertebral column. They are temporary structures, and are sometimes 
called the primordial kidneys. The Wolffian bodies consist of tubules 



DEVELOPMENT OF THE EMBRYO. 131 

which run transversely and are lined with epithelium ; internally they 
become invaginated to receive tufts of blood vessels ; externally they open 
into a common excretory duct, the duct of the Wolffian body, which unites 
with the duct of the opposite body, and empties into the intestinal canal 
at a point opposite the allantois. On the outer side of the Wolffian body 
there appears another duct, the duct of Miiller, which also opens into the 
intestine. 

Behind the Wolffian bodies are developed the structures which become 
either the ovaries or testicles. In the development of the female, the 
Wolffian bodies and their ducts disappear; the extremities of the Miillerian 
ducts dilate and form the fimbriated extremity of the Fallopian tubes, while 
the lower portions coalesce to form the body of the uterus and vagina, 
which now separate themselves from the intestine. 

In the development of the male, the Miillerian ducts atrophy, and the 
ducts of the Wolffian body ultimately form the epididymis and vas deferens. 
About the seventh month the testicles begin to descend, and by the ninth 
month have passed through the abdominal ring into the scrotum. 

The Kidneys are developed out of the Wolffian bodies. They consist of 
little pyramidal lobules, composed of tubules which open at the apex into 
the pelvis. As they pass outward they become convoluted and cup-shaped 
at their extremities, receive a tuft of blood vessels, and form the Malpig- 
hian bodies. 

The ureters are developed from the kidneys, and pass downward to be 
connected with the bladder. 

The Circulatory Apparatus assumes three different forms at different 
periods of life, all having reference to the manner in which the embryo 
receives nutritious matter and is freed of waste products. 

The Vitelline circulation appears first and absorbs nutritious material 
from the vitellus. It is formed by blood vessels which emerge from the 
body and ramify over a portion of the vitelline membrane constituting the 
area vasculosa. The heart, lying in the median line, gives off two arches 
which unite to form the abdominal aorta, from which two large arteries 
are given off, passing into the vascular area ; the venous blood is returned 
by veins which enter the heart. These vessels are known as the omphalo- 
mesenteric arteries and veins. The vitelline circulation is of short dura- 
tion in the mammals, as the supply of nutritious matter in the vitellus soon 
becomes exhausted. 

The Placental circulation becomes established when the blood vessels in 
the allantois enter the villous processes of the chorion and come into close 
relationship with the maternal blood vessels. This circulation lasts during 



132 HUMAN PHYSIOLOGY. 

the whole of intra-uterine Ine, but gives way at birth to the adult circula- 
tion, the change being made possible by the development of the circulatory 
apparatus. 

The Heart appears as a mass of cells coming off from the anterior por- 
tion of the intestine ; its central part liquefies, and pulsations soon begin. 
The heart is at first tubular, receiving posteriorly the venous trunks and 
giving off anteriorly the arterial trunks. It soon becomes twisted upon 
itself, so that the two extremities lie upon the same plane. 

The heart now consists of a single auricle and a single ventricle. A . 
septum growing from the apex of the ventricle, divides it into two cavities, 
a right and a left. The auricles also become partly separated by a septum 
which is perforated by the foramen ovale. The arterial trunk becomes 
separated by a partition, into two canals, which become, ultimately, the 
aorta and pulmonary artery. The auricles are separated from the Ventri- 
cles by incomplete septa, through which the blood passes into the ventricles. 

Arteries. The aorta arises, from the cephalic extremity of the heart and 
divides into* two branches which ascend, one on each side of the intestine, 
and unite posteriorly to form the main aorta; posteriorly to these first 
aortic arches four others are developed, so that there -are five altogether 
running along the visceral arches. The two anterior SGon disappear. The 
third arch becomes the internal carotid and the external carotid ; a part 
of the fourth arch, on the right side, becomes the subclavian artery, and 
the remainder atrophies and disappears, but on the left side it enlarges and 
becomes the permanent aorta; the fifth arch becomes the pulmonary artery 
on the left side. The communication between the pulmonary artery and 
the aorta, the ductus arteriosus ', disappears at an early period. 

Veins. The venous system appears first as two short, transverse veins, 
the canals of Cuvier, formed by the union of the vertebral veins and the 
cardinal veins, which empty into the auricle. The inferior vena cava is 
formed as the kidneys develop, by the union of the renal veins, which, in 
a short time, receive branches from the lower extremities. The sub- 
clavian veins join the jugular as the upper extremeties develop. The heart 
descends in the thorax, and the canals of Cuvier become oblique ; they 
shortly communicate by a transverse duct, which ultimately becomes the 
left innominate vein. The left canal of Cuvier atrophies and becomes a 
fibrous cord. A transverse branch now appears, which carries the blood 
from the left cardinal vein into the right, and becomes the vena azygos 
minor; the right cardinal vein becomes the vena azygos major. 

Circulation of Blood in the Fcetus. The blood returning from the 
placenta, after having received oxygen, and been freed from carbonic acid, is 



DEVELOPMENT OF THE EMBRYO. 133 

carried by the umbilical vein to the ■ under surface of the liver ; here a 
portion of it passes through the" ductus venosus into the ascending vena 
cava, while the remainder flows through the liver, and passes into the vena 
cava by the hepatic veins. When the blood is emptied into the right 
auricle, it is directed by the Eustachian valve, through the foramen ovale, 
into the left auricle, thence into the left ventricle, and so into the aorta to 
all parts of the system. The venous blood returning from the head and 
upper extremities is emptied, by the superior vena cava, into the right 
auricle, from which it passes into the right ventricle, and thence into the 
pulmonary artery. Owing to the condition of the lung, only a small por- 
tion flows through the pulmonary capillaries, the greater part passing 
through the ductus arteriosus, which opens into the aorta at a point below 
the origin of the carotid and subclavian arteries. The mixed blood now 
passes down the aorta to supply the lower extremities, but a portion of 
it is directed, by the hypogastric arteries, to the placenta, to be again 
oxygenated. 

At birth, the placental circulation gives way to the circulation of the 
adult. As soon as the child begins to breathe, the lungs expand, blood 
flows freely through the pulmonary capillaries, and the ductus arteriosus 
begins to contract. The foramen ovale closes about the tenth day. The 
umbilical vein, the ductus venosus, and the hypogastric arteries become 
impervious in several days, and ultimately form rounded cords. 



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